Golf balls having a core with surrounding intermediate foam layer

ABSTRACT

Multi-layered golf balls having a core, intermediate layer, and cover are provided. The ball includes a non-foamed inner core (center) made of a thermoplastic or thermoset composition such as polybutadiene rubber. An intermediate layer comprising a foamed composition, such as polyurethane foam, is disposed about the inner core. The foamed intermediate layer may have a specific gravity gradient within the layer, wherein the outer surface specific gravity is greater than the midpoint specific gravity. Ball constructions having two intermediate layers, wherein at least one layer is a foamed layer can be made. A cover having at least one layer is disposed about the intermediate layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending, co-assigned U.S. patentapplication Ser. No. 15/830,091, filed on Dec. 4, 2017, now allowed,which is a continuation-in-part of co-assigned U.S. patent applicationSer. No. 15/071,381, filed on Mar. 16, 2016, now U.S. Pat. No. 9,937,385the entire disclosures of which are incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to multi-piece, golf balls madeof non-foamed and foamed compositions. In one embodiment, a non-foamedsingle or dual core is made and a foamed composition, for example,polyurethane foam, is cast over the core to form an intermediate layer.The ball further includes a cover of at least one layer. The core,intermediate, and cover layers may have different properties, forexample, flex modulus, hardness, and specific gravity values.

Brief Review of the Related Art

Both professional and amateur golfer use multi-piece, solid golf ballstoday. Basically, a two-piece solid golf ball includes a solid innercore protected by an outer cover. Normally, the inner core is made of anatural or synthetic rubber such as polybutadiene, styrene butadiene, orpolyisoprene. The cover surrounds the inner core and may be made of avariety of materials including ethylene acid copolymer ionomers,polyamides, polyesters, polyurethanes, and polyureas.

In recent years, three-piece, four-piece, and even five-piece balls havebecome more popular. New manufacturing technologies, lower materialcosts, and desirable ball playing performance properties havecontributed to these multi-piece balls becoming more popular. Many golfballs used today have multi-layered cores comprising an inner core andat least one surrounding outer core layer. For example, the inner coremay be made of a relatively soft and resilient material, while the outercore may be made of a harder and more rigid material. The “dual-core”subassembly is encapsulated by a cover of at least one layer to make afinished ball. Different materials can be used to manufacture the coreand cover layers and provide various properties to the finished ball.

In general, dual-cores comprising an inner core (or center) and asurrounding outer core layer are known in the industry. For example,Chikaraishi et al., U.S. Pat. No. 5,048,838 discloses a three-piece golfball containing a two-piece solid core and a cover. The dense inner corehas a diameter in the range of 15-25 mm with a specific gravity of 1.2to 4.0 and the outer core layer has a specific gravity of 0.1 to 3.0less than the specific gravity of the inner core. The inner and outercores are made of rubber compositions. Watanabe, U.S. Pat. No. 7,160,208discloses a three-piece golf ball comprising a rubber-based inner core;a rubber-based outer core layer; and a polyurethane elastomer-basedcover. The inner core layer has a JIS-C hardness of 50 to 85; the outercore layer has a JIS-C hardness of 70 to 90; and the cover has a Shore Dhardness of 46 to 55. Also, the inner core has a specific gravity ofmore than 1.0, and the core outer layer has a specific gravity equal toor greater than that of that of the inner core.

The core sub-structure located inside of the golf ball acts as an engineor spring for the ball. Thus, the composition and construction of thecore is a key factor in determining the resiliency and reboundingperformance of the ball. In general, the rebounding performance of theball is determined by calculating its initial velocity after beingstruck by the face of the golf club and its outgoing velocity aftermaking impact with a hard surface. More particularly, the “Coefficientof Restitution” or “COR” of a golf ball refers to the ratio of a ball'srebound velocity to its initial incoming velocity when the ball is firedout of an air cannon into a rigid vertical plate. The COR for a golfball is written as a decimal value between zero and one. A golf ball mayhave different COR values at different initial velocities. The UnitedStates Golf Association (USGA) sets limits on the initial velocity ofthe ball so one objective of golf ball manufacturers is to maximize CORunder such conditions. Balls with a higher rebound velocity have ahigher COR value. Such golf balls rebound faster, retain more totalenergy when struck with a club, and have longer flight distance asopposed to balls with low COR values. These properties are particularlyimportant for long distance shots. For example, balls having highresiliency and COR values tend to travel a far distance when struck by adriver club from a tee.

The durability, spin rate, and feel of the ball also are importantproperties. In general, the durability of the ball refers to theimpact-resistance of the ball. Balls having low durability appear wornand damaged even when such balls are used only for brief time periods.In some instances, the cover may be cracked or torn. The spin raterefers to the ball's rate of rotation after it is hit by a club. Ballshaving a relatively high spin rate are advantageous for short distanceshots made with irons and wedges. Professional and highly skilledamateur golfers can place a back spin more easily on such balls. Thishelps a player better control the ball and improves shot accuracy andplacement. By placing the right amount of spin on the ball, the playercan get the ball to stop precisely on the green or place a fade on theball during approach shots. On the other hand, recreational players whocannot intentionally control the spin of the ball when hitting it with aclub are less likely to use high spin balls. For such players, the ballcan spin sideways more easily and drift far-off the course, especiallyif it is hooked or sliced. Meanwhile, the “feel” of the ball generallyrefers to the sensation that a player experiences when striking the ballwith the club and it is a difficult property to quantify. Most playersprefer balls having a soft feel, because the player experience a morenatural and comfortable sensation when their club face makes contactwith these balls. Balls having a softer feel are particularly desirablewhen making short shots around the green, because the player senses morewith such balls. The feel of the ball primarily depends upon thehardness and compression of the ball.

Manufacturers of golf balls are constantly looking to differentmaterials and ball constructions for improving the playing performanceand other properties of the ball. For example, hard and durablematerials having a relatively high flex modulus can be used to make arelatively hard core. The resulting golf ball tends to travel a longdistance because of the high velocity imparted by the hard core.However, one disadvantage with these harder balls is they tend toprovide the golfer with a rougher and harder “feel.” Thus, the playermay experience a more uncomfortable and unnatural sensation as the clubface makes impact with the ball. Moreover, the player tends to have lesscontrol when hitting relatively hard balls. It generally is moredifficult to hit hard balls with the proper touch and spin.

To address these problems, golf ball manufacturers have looked at softerand lighter-weight materials, such as foams, for making the inner core.For example, Puckett and Cadorniga, U.S. Pat. Nos. 4,836,552 and4,839,116 disclose one-piece, short distance golf balls made of a foamcomposition comprising a thermoplastic polymer (ethylene acid copolymerionomer such as Surlyn®) and filler material (microscopic glassbubbles). The density of the composition increases from the center tothe surface of the ball. Thus, the ball has relatively dense outer skinand a cellular inner core. According to the '552 and '116 patents, byproviding a short distance golf ball, which will play approximately 50%of the distance of a conventional golf ball, the land requirements for agolf course can be reduced 67% to 50%.

Gentiluomo, U.S. Pat. No. 5,104,126 discloses a three-piece ball with adense inner core made of steel, lead, brass, zinc, copper, and a filledelastomer, wherein the core has a specific gravity of at least 1.25. Theinner core is encapsulated by a lower density syntactic foamcomposition, and the core construction is encapsulated by an ionomercover. Yabuki et al., U.S. Pat. No. 5,482,285 discloses a three-piecegolf ball having an inner core and outer core encapsulated by an ionomercover. The specific gravity of the outer core is reduced so that itfalls within the range of 0.2 to 1.0. The specific gravity of the innercore is adjusted accordingly so that the total weight of the inner/outercore falls within a range of 32.0 to 39.0 g. The inner core may beformed of a rubber composition and the outer core may be formed of afoamed resin such as an ionomer polyethylene, or polystyrene resin, or athermosetting resin such as a phenol resin.

Aoyama, U.S. Pat. Nos. 5,688,192 and 5,823,889 disclose a golf ballcontaining a core, wherein the core comprises an inner and outerportion, and a cover made of a material such as balata rubber orethylene acid copolymer ionomer. The core is made by foaming, injectinga compressible material, gasses, blowing agents, or gas-containingmicrospheres into polybutadiene or other core material. According to the'889 patent, polyurethane compositions may be used. The compressiblematerial, for example, gas-containing compressible cells may bedispersed in a limited part of the core so that the portion containingthe compressible material has a specific gravity of greater than 1.00.

Sullivan and Binette, U.S. Pat. No. 5,833,553 discloses a golf ballhaving core with a coefficient of restitution of at least 0.650 and acover with a thickness of at least 3.6 mm (0.142 inches) and a Shore Dhardness of at least 60. According to the '553 patent, the combinationof a soft core with a thick, hard cover results in a ball having betterdistance. The '553 patent discloses that the core may be formed from auniform composition or may be a dual or multi-layer core, and it may befoamed or unfoamed. Polybutadiene rubber, natural rubber, metallocenecatalyzed polyolefins, and polyurethanes are described as being suitablematerials for making the core.

Sullivan and Ladd, U.S. Pat. No. 6,688,991 discloses a golf ballcontaining a low specific gravity core and an optional intermediatelayer. This subassembly is encased within a high specific gravity coverwith Shore D hardness in the range of about 40 to about 80. The core ispreferably made from a highly neutralized thermoplastic polymer such asethylene acid copolymer which has been foamed. The cover preferably hashigh specific gravity fillers dispersed therein.

Nesbitt, U.S. Pat. No. 6,767,294 discloses a golf ball comprising: i) apressurized foamed inner center formed from a thermoset material, athermoplastic material, or combinations thereof, a blowing agent and across-linking agent and, ii) an outer core layer formed from a secondthermoset material, a thermoplastic material, or combinations thereof.Additionally, a barrier resin or film can be applied over the outer corelayer to reduce the diffusion of the internal gas and pressure from thenucleus (center and outer core layer). Preferred polymers for thebarrier layer have low permeability such as Saran® film (poly(vinylidene chloride), Barex® resin (acyrlonitrile-co-methyl acrylate),poly (vinyl alcohol), and PET film (polyethylene terephthalate). The'294 patent does not disclose core layers having different hardnessgradients.

Sullivan, Ladd, and Hebert, U.S. Pat. No. 7,708,654 discloses a golfball having a foamed intermediate layer. Referring to FIG. 1 in the '654patent, the golf ball includes a core (12), an intermediate layer (14)made of a highly neutralized polymer having a reduced specific gravity(less than 0.95), and a cover (16). According to the '654 patent, theintermediate layer can be an outer core, a mantle layer, or an innercover. The reduction in specific gravity of the intermediate layer iscaused by foaming the composition of the layer and this reduction can beas high as 30%. The '654 patent discloses that other foamed compositionssuch as foamed polyurethanes and polyureas may be used to form theintermediate layer.

Tutmark, U.S. Pat. No. 8,272,971 is directed to golf balls containing anelement that reduces the distance of the ball's flight path. In oneembodiment, the ball includes a core and cover. A cavity is formedbetween core and cover and this may be filled by a foamed polyurethane“middle layer” in order to dampen the ball's flight properties. The foamof the middle layer is relatively light in weight; and the core isrelatively heavy and dense. According to the '971 patent, when a golferstrikes the ball with a club, the foam in the middle layer actuates andcompresses, thereby absorbing much of the impact from the impact of theball.

Although some foam constructions for golf balls have been consideredover the years, there are drawbacks with using some foam materials. Forexample, some polymer materials are difficult to foam. Once the materialis converted into foam, the foamed material may suffer from loss ofimpact durability. Also, it can be difficult to adjust the specificgravity of some foamed materials without losing impact durability,toughness, resiliency (rebounding performance), and the like. Golf ballsare exposed to a wide range of high and low temperatures during theirlife span. If the chemical and physical properties of the foamedcomposition change, the properties of the resulting golf ball core maybe adversely affected. For example, there may be a negative impact onthe size, resiliency, and hardness of the ball.

In view of some of the disadvantages with some foam compositions, itwould be desirable to have new compositions and ball constructionsincluding foamed layers with good stability. The resulting foamed layersshould have good resiliency and impact durability over a widetemperature range. The specific gravity of the foamed layers should beeasy to adjust without a loss in desirable properties. For example, thefoamed layers should have high impact durability at high and lowspecific gravity levels. The present invention provides new foamcompositions and golf ball constructions having such properties,features, and other benefits.

SUMMARY OF THE INVENTION

The present invention provides a multi-layered golf ball comprising acore comprising an inner core (center); outer core layer; and coverhaving at least one layer. In one version, the ball includes a coresubassembly comprising: i) an inner core comprising a non-foamedthermoset or thermoplastic composition, wherein the inner core has adiameter in the range of about 0.750 to about 1.500 inches, and ii) anintermediate layer comprising a foamed composition, wherein the outercore layer is disposed about the inner core and has a thickness in therange of about 0.025 to about 0.800 inches. Preferably, the foamedintermediate layer is made from a foamed thermoset composition.

Non-foamed thermoset or thermoplastic materials are used to form theinner core. For example, polybutadiene rubber may be used. While, foamedcompositions are used to form the intermediate layer. In one version,the intermediate layer comprises a foamed polyurethane compositionprepared from a mixture comprising polyisocyanate, polyol, and curingagent compounds, and blowing agent. Aromatic and aliphaticpolyisocyanates may be used. The foamed polyurethane composition may beprepared by using water as a blowing agent. The water is added to themixture in a sufficient amount to cause the mixture to foam.Surfactants, catalysts, mineral fillers, and other additives may beincluded in the mixture.

A cover having single or multiple layers is disposed about theintermediated layer. For example, a cover layer can be prepared from anionomer composition comprising an O/X/Y-type copolymer, wherein O isα-olefin, X is a C₃-C₈ α,β-ethylenically unsaturated carboxylic acid,and Y is an acrylate selected from alkyl acrylates and aryl acrylates,wherein greater than 70% of the acid groups are neutralized with a metalion. Polyurethane, polyurea and polyurethane/polyurea hybrid covers alsocan be prepared.

The core and intermediate layers may have different hardness gradients.For example, the inner core can have a positive hardness gradient; andthe intermediate layer can have a positive hardness gradient. In asecond embodiment, the inner core has a zero or negative hardnessgradient, and the intermediate layer has a positive hardness gradient.

The inner core has a specific gravity and intermediate layer has aspecific gravity. Preferably, the specific gravity of the inner core isgreater than the specific gravity of the intermediate layer. Further, inone preferred embodiment, the intermediate layer has a specific gravitygradient, wherein the intermediate layer has an outer surface specificgravity and a midpoint specific gravity, the outer surface specificgravity being greater than the midpoint specific gravity.

In yet another embodiment, there are two intermediate layers. A firstintermediate layer is disposed about the core and a second intermediatelayer is located adjacent to the first intermediate layer, wherein atleast one of the intermediate layers comprises a foamed thermosetcomposition. For example, the first intermediate layer can comprise thefoamed thermoset composition. In another example, the secondintermediate layer can comprise the foamed thermoset composition. In yetanother example, both the first and second intermediate layers cancomprise foamed thermoset compositions.

Foamed thermoplastic compositions also can be used to form the foamedintermediate layer. For example, the intermediate layer can comprise afoamed thermoplastic polymer selected from the group consisting ofpartially-neutralized ethylene acid copolymer ionomers;highly-neutralized ethylene acid copolymer ionomers; polyesters;polyamides; polyamide-ethers, polyamide-esters; polyurethanes,polyureas; fluoropolymers; polystyrenes; polypropylenes; polyethylenes;polyvinyl chlorides; polyvinyl acetates; polycarbonates; polyvinylalcohols; polyester-ethers; polyethers; polyimides, polyetherketones,polyamideimides; and mixtures thereof. Preferably, the thermoplasticpolymer is selected from partially-neutralized ethylene acid copolymerionomers; highly-neutralized ethylene acid copolymer ionomers; andmixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims. However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a dual-layered core subassembly madein accordance with the present invention;

FIG. 2 is a cross-sectional view of a three-piece golf ball having adual-layered core made in accordance with the present invention;

FIG. 3 is a cross-sectional view of a four-piece golf ball having adual-layered core made in accordance with the present invention;

FIG. 4 is a perspective view of a finished golf ball made in accordancewith the present invention;

FIG. 5 is a is a cross-sectional view of a dual-core assembly includingan inner core and surrounding outer core layer showing a foamedgeometric midpoint, outer region, and outer surface skin in the outercore, the core assembly being made in accordance with the presentinvention; and

FIG. 6 is a is a cross-sectional view of a dual-core assembly includingan inner core and surrounding outer core layer showing a foamedgeometric midpoint, partially-collapsed foamed outer region, and outersurface skin; and a surrounding inner cover layer, the core assembly andinner cover being made in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Golf Ball Constructions

Golf balls having various constructions may be made in accordance withthis invention. For example, golf balls having three piece, four-piece,and five-piece constructions with single or multi-layered covermaterials may be made. Representative illustrations of such golf ballconstructions are provided and discussed further below. The term,“layer” as used herein means generally any spherical portion of the golfball. More particularly, in one version, a three-piece golf ballcontaining a core, intermediate layer, and single-layered cover is made.As used herein, the term, “intermediate layer” means a layer of the balldisposed between the core and cover. The intermediate layer also may bereferred to as a mantle or casing layer. In another embodiment, afour-piece ball containing a dual-core, intermediate layer, andsingle-layered cover is made. The dual-core includes an inner core(center) and surrounding outer core layer. In another version, afive-piece golf ball containing a dual-core, intermediate layer, anddual-cover (inner cover and outer cover layers) is made. Six-piece ballsalso can be made. The diameter and thickness of the different layersalong with properties such as hardness and compression may varydepending upon the construction and desired playing performanceproperties of the golf ball.

Inner Core Composition

As discussed above, the golf ball preferably contains an inner core(center) made from a non-foamed composition. In one preferredembodiment, the inner core is made from a non-foamed thermosetcomposition and more preferably from a non-foamed thermoset rubbercomposition. In another embodiment, a two-layered or dual-core isconstructed, wherein the inner core (center) is surrounded by an outercore layer.

Suitable thermoset rubber materials that may be used to form the innercore layer (center) include, but are not limited to, polybutadiene,polyisoprene, ethylene propylene rubber (“EPR”),ethylene-propylene-diene (“EPDM”) rubber, styrene-butadiene rubber,styrenic block copolymer rubbers (such as “SI”, “SIS”, “SB”, “SBS”,“SIBS”, and the like, where “S” is styrene, “I” is isobutylene, and “B”is butadiene), polyalkenamers such as, for example, polyoctenamer, butylrubber, halobutyl rubber, polystyrene elastomers, polyethyleneelastomers, polyurethane elastomers, polyurea elastomers,metallocene-catalyzed elastomers and plastomers, copolymers ofisobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and blends of two or morethereof. In another embodiment, a two-layered or dual-core isconstructed, wherein the inner core (center) is surrounded by an outercore layer. Preferably, the inner core and outer core layers are bothformed from a polybutadiene rubber composition.

The thermoset rubber composition may be cured using conventional curingprocesses. Suitable curing processes include, for example,peroxide-curing, sulfur-curing, high-energy radiation, and combinationsthereof. Preferably, the rubber composition contains a free-radicalinitiator selected from organic peroxides, high energy radiation sourcescapable of generating free-radicals, and combinations thereof. In onepreferred version, the rubber composition is peroxide-cured. Suitableorganic peroxides include, but are not limited to, dicumyl peroxide;n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. In aparticular embodiment, the free radical initiator is dicumyl peroxide,including, but not limited to Perkadox® BC, commercially available fromAkzo Nobel. Peroxide free-radical initiators are generally present inthe rubber composition in an amount of at least 0.05 parts by weight per100 parts of the total rubber, or an amount within the range having alower limit of 0.05 parts or 0.1 parts or 1 part or 1.25 parts or 1.5parts or 2.5 parts or 5 parts by weight per 100 parts of the totalrubbers, and an upper limit of 2.5 parts or 3 parts or 5 parts or 6parts or 10 parts or 15 parts by weight per 100 parts of the totalrubber. Concentrations are in parts per hundred (phr) unless otherwiseindicated. As used herein, the term, “parts per hundred,” also known as“phr” or “pph” is defined as the number of parts by weight of aparticular component present in a mixture, relative to 100 parts byweight of the polymer component. Mathematically, this can be expressedas the weight of an ingredient divided by the total weight of thepolymer, multiplied by a factor of 100.

The rubber compositions may further include a reactive cross-linkingco-agent. Suitable co-agents include, but are not limited to, metalsalts of unsaturated carboxylic acids having from 3 to 8 carbon atoms;unsaturated vinyl compounds and polyfunctional monomers (e.g.,trimethylolpropane trimethacrylate); phenylene bismaleimide; andcombinations thereof. Particular examples of suitable metal saltsinclude, but are not limited to, one or more metal salts of acrylates,diacrylates, methacrylates, and dimethacrylates, wherein the metal isselected from magnesium, calcium, zinc, aluminum, lithium, and nickel.In a particular embodiment, the co-agent is selected from zinc salts ofacrylates, diacrylates, methacrylates, and dimethacrylates. In anotherparticular embodiment, the agent is zinc diacrylate (ZDA). When theco-agent is zinc diacrylate and/or zinc dimethacrylate, the co-agent istypically included in the rubber composition in an amount within therange having a lower limit of 1 or 5 or 10 or 15 or 19 or 20 parts byweight per 100 parts of the total rubber, and an upper limit of 24 or 25or 30 or 35 or 40 or 45 or 50 or 60 parts by weight per 100 parts of thebase rubber.

Radical scavengers such as a halogenated organosulfur, organicdisulfide, or inorganic disulfide compounds may be added to the rubbercomposition. These compounds also may function as “soft and fastagents.” As used herein, “soft and fast agent” means any compound or ablend thereof that is capable of making a core: 1) softer (having alower compression) at a constant “coefficient of restitution” (COR);and/or 2) faster (having a higher COR at equal compression), whencompared to a core equivalently prepared without a soft and fast agent.Preferred halogenated organosulfur compounds include, but are notlimited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zincpentachlorothiophenol (ZnPCTP). Using PCTP and ZnPCTP in golf ball innercores helps produce softer and faster inner cores. The PCTP and ZnPCTPcompounds help increase the resiliency and the coefficient ofrestitution of the core. In a particular embodiment, the soft and fastagent is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyldisulfide, dixylyl disulfide, 2-nitroresorcinol, and combinationsthereof.

In addition, the rubber compositions may include antioxidants. Also,processing aids such as high molecular weight organic acids and saltsthereof may be added to the composition. Other ingredients such asaccelerators, dyes and pigments, wetting agents, surfactants,plasticizers, coloring agents, fluorescent agents, stabilizers,softening agents, impact modifiers, antiozonants, as well as otheradditives known in the art may be added to the rubber composition. Therubber composition also may include filler(s) such as materials selectedfrom carbon black, clay and nanoclay particles as discussed above, talc(e.g., Luzenac HAR® high aspect ratio talcs, commercially available fromLuzenac America, Inc.), glass (e.g., glass flake, milled glass, andmicroglass), mica and mica-based pigments (e.g., Iriodin® pearl lusterpigments, commercially available from The Merck Group), and combinationsthereof. Metal fillers such as, for example, particulate; powders;flakes; and fibers of copper, steel, brass, tungsten, titanium,aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin, zinc,barium, bismuth, bronze, silver, gold, and platinum, and alloys andcombinations thereof also may be added to the rubber composition toadjust the specific gravity of the composition as needed. As discussedabove, the inner core layer preferably has a specific gravity (density)greater than the inner core layer's specific gravity. Thus, metal orother fillers may be added to the polybutadiene rubber composition (orother thermoset material) used to form the inner core layer in asufficient amount so the specific gravity of the inner core remainsgreater than the specific gravity of the outer core.

Examples of commercially-available polybutadiene rubbers that can beused in accordance with this invention, include, but are not limited to,BR 01 and BR 1220, available from BST Elastomers of Bangkok, Thailand;SE BR 1220LA and SE BR1203, available from DOW Chemical Co of Midland,Mich.; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear, Incof Akron, Ohio; BR 01, 51 and 730, available from Japan Synthetic Rubber(JSR) of Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29MES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221,available from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available fromLG Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B, BR150L,BR230, BR360L, BR710, and VCR617, available from UBE Industries, Ltd. ofTokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AF and P30AF, andEUROPRENE BR HV80, available from Polimeri Europa of Rome, Italy; AFDENE50 and NEODENE BR40, BR45, BR50 and BR60, available from Karbochem (PTY)Ltd. of Bruma, South Africa; KBR 01, NdBr 40, NdBR-45, NdBr 60, KBR710S, KBR 710H, and KBR 750, available from Kumho Petrochemical Co.,Ltd. Of Seoul, South Korea; and DIENE 55NF, 70AC, and 320 AC, availablefrom Firestone Polymers of Akron, Ohio.

The polybutadiene rubber is used in an amount of at least about 5% byweight based on total weight of composition and is generally present inan amount of about 5% to about 100%, or an amount within a range havinga lower limit of 5% or 10% or 20% or 30% or 40% or 50% and an upperlimit of 55% or 60% or 70% or 80% or 90% or 95% or 100%. Preferably, theconcentration of polybutadiene rubber is about 40 to about 95 weightpercent. If desirable, lesser amounts of other thermoset materials maybe incorporated into the base rubber. Such materials include the rubbersdiscussed above, for example, cis-polyisoprene, trans-polyisoprene,balata, polychloroprene, polynorbornene, polyoctenamer, polypentenamer,butyl rubber, EPR, EPDM, styrene-butadiene, and the like.

As discussed above, in one preferred embodiment, a thermoset rubbercomposition is used to form the inner core. In alternative embodiments,the inner core layer is made from a thermoplastic material, for example,an ethylene acid copolymer ionomer composition. Other suitablethermoplastic polymers that may be used to form the inner core layerinclude, but are not limited to, the following polymers (includinghomopolymers, copolymers, and derivatives thereof.) (a) polyesters,particularly those modified with a compatibilizing group such assulfonate or phosphonate, including modified poly(ethyleneterephthalate), modified poly(butylene terephthalate), modifiedpoly(propylene terephthalate), modified poly(trimethyleneterephthalate), modified poly(ethylene naphthenate), and those disclosedin U.S. Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entiredisclosures of which are hereby incorporated herein by reference, andblends of two or more thereof; (b) polyamides, polyamide-ethers, andpolyamide-esters, and those disclosed in U.S. Pat. Nos. 6,187,864,6,001,930, and 5,981,654, the entire disclosures of which are herebyincorporated herein by reference, and blends of two or more thereof; (c)polyurethanes, polyureas, polyurethane-polyurea hybrids, and blends oftwo or more thereof; (d) fluoropolymers, such as those disclosed in U.S.Pat. Nos. 5,691,066, 6,747,110 and 7,009,002, the entire disclosures ofwhich are hereby incorporated herein by reference, and blends of two ormore thereof; (e) polystyrenes, such as poly(styrene-co-maleicanhydride), acrylonitrile-butadiene-styrene, poly(styrene sulfonate),polyethylene styrene, and blends of two or more thereof; (f) polyvinylchlorides and grafted polyvinyl chlorides, and blends of two or morethereof; (g) polycarbonates, blends ofpolycarbonate/acrylonitrile-butadiene-styrene, blends ofpolycarbonate/polyurethane, blends of polycarbonate/polyester, andblends of two or more thereof; (h) polyethers, such as polyaryleneethers, polyphenylene oxides, block copolymers of alkenyl aromatics withvinyl aromatics and polyamicesters, and blends of two or more thereof;(i) polyimides, polyetherketones, polyamideimides, and blends of two ormore thereof; and (j) polycarbonate/polyester copolymers and blends.

It also is recognized that thermoplastic materials can be “converted”into thermoset materials by cross-linking the polymer chains so theyform a network structure, and such cross-linked thermoplastic materialsmay be used to form the inner cover layers in accordance with thisinvention. For example, thermoplastic polyolefins such as linear lowdensity polyethylene (LLDPE), low density polyethylene (LDPE), and highdensity polyethylene (HDPE) may be cross-linked to form bonds betweenthe polymer chains. The cross-linked thermoplastic material typicallyhas improved physical properties and strength over non-cross-linkedthermoplastics, particularly at temperatures above the crystallinemelting point. Preferably a partially or fully-neutralized ionomer, asdescribed above, is covalently cross-linked to render it into athermoset composition (that is, it contains at least some level ofcovalent, irreversable cross-links). Thermoplastic polyurethanes andpolyureas also may be converted into thermoset materials in accordancewith the present invention.

Modifications in the thermoplastic polymeric structure of thermoplasticscan be induced by a number of methods, including exposing thethermoplastic material to high-energy radiation or through a chemicalprocess using peroxide. Radiation sources include, but are not limitedto, gamma-rays, electrons, neutrons, protons, x-rays, helium nuclei, orthe like. Gamma radiation, typically using radioactive cobalt atoms andallows for considerable depth of treatment, if necessary. For corelayers requiring lower depth of penetration, electron-beam acceleratorsor UV and IR light sources can be used. Useful UV and IR irradiationmethods are disclosed in U.S. Pat. Nos. 6,855,070 and 7,198,576, whichare incorporated herein by reference. The thermoplastic core layers maybe irradiated at dosages greater than 0.05 Mrd, preferably ranging from1 Mrd to 20 Mrd, more preferably from 2 Mrd to 15 Mrd, and mostpreferably from 4 Mrd to 10 Mrd. In one preferred embodiment, the coresare irradiated at a dosage from 5 Mrd to 8 Mrd and in another preferredembodiment, the cores are irradiated with a dosage from 0.05 Mrd to 3Mrd, more preferably 0.05 Mrd to 1.5 Mrd.

The cross-linked thermoplastic material may be created by exposing thethermoplastic to: 1) a high-energy radiation treatment, such as electronbeam or gamma radiation, such as disclosed in U.S. Pat. No. 5,891,973,which is incorporated by reference herein, 2) lower energy radiation,such as ultra-violet (UV) or infra-red (IR) radiation; 3) a solutiontreatment, such as an isocyanate or a silane; 4) incorporation ofadditional free radical initiator groups in the thermoplastic prior tomolding; and/or 5) chemical modification, such as esterification orsaponification, to name a few.

Outer Core Composition

As discussed above, the inner core may be formed from thermoset orthermoplastic materials and is preferably formed from a non-foamedthermoset rubber. In one embodiment, a dual-core subassembly having aninner core and surrounding outer core layer is formed. The outer corelayer also may be formed from thermoset or thermoplastic materials. Inone preferred embodiment, both the inner core and outer core layers areformed from a thermoset rubber composition. That is, the inner core maybe formed from a first thermoset rubber composition; and the outer corelayer may be formed from a second thermoset rubber composition.

In one embodiment, the inner and outer core layers have the samespecific gravity levels. In a second embodiment, the specific gravity ofthe inner core is greater than the specific gravity of the outer corelayer. Finally, in a third embodiment, the specific gravity of the innercore is less than the specific gravity of the outer core layer. Thus,both the inner and outer core layers may be formed from a polybutadienerubber composition. The rubber compositions may contain conventionaladditives such as free-radical initiators, cross-linking agents, softand fast agents, and antioxidants, and the composition may be curedusing conventional systems as described above. If, in one example, theobjective is to make the specific gravities of the inner core and outercore layers different, the concentration and/or type of metal fillersused in the respective compositions may be adjusted to achieve thisresult. For example, the outer core layer may contain a relatively smallconcentration of metal fillers, while the inner core contains a largeconcentration of metal fillers.

Intermediate Layer Composition

In the present invention, the inner core (center) preferably comprises anon-foamed thermoset or thermoplastic polymer composition. As discussedabove, dual-core sub-assemblies including an inner core and outer corelayer also can be made. Meanwhile, the intermediate layer, whichsurrounds the inner core or dual-core sub-assembly, preferably comprisesa foamed thermoset or thermoplastic composition. Referring to FIG. 1,one version of a ball sub-assembly comprising an inner core and foamedintermediate layer that can be made in accordance with this invention isgenerally indicated at (10). The sub-assembly (10) includes a non-foamedinner core (center) (12) and a surrounding foamed intermediate layer(14). The dual-core is used to construct a golf ball as shown in FIG. 2.Here, the golf ball (16) contains a sub-assembly (18) having a center(18 a) and intermediate layer (18 b) surrounded by a single-layeredcover (19). In another version, referring to FIG. 3, the golf ball (20)contains a dual-core (22) having a center (22 a) and outer core layer(22 b). The dual-core (22) is surrounded by a multi-layered structure(26) having an intermediate layer (26 a) and outer cover layer (26 b).

The foamed composition used to form the intermediate layer may have anopen or closed cellular structure or combinations thereof and the foamstructure may range from relatively rigid foam to very flexible foam.The hardness, flex modulus, specific gravity, and other properties ofthe foamed intermediate layer can be adjusted as needed. One key featureof the present invention is the specific gravity of the foamedintermediate layer can be adjusted without sacrificing the impactdurability of the layer and finished ball. For example, the specificgravity of the foamed intermediate layer can be adjusted so the layerhas a relatively low specific gravity or a relatively high specificgravity, while maintaining toughness, impact durability, and resiliency.The different specific gravity levels of the foamed intermediate layerare discussed further below.

In general, foam compositions are made by forming gas bubbles in apolymer mixture using a foaming (blowing) agent. As the bubbles form,the mixture expands and forms a foam composition that can be molded intoan end-use product having either an open or closed cellular structure.Flexible foams generally have an open cell structure, where the cellswalls are incomplete and contain small holes through which liquid andair can permeate. Such flexible foams are used traditionally forautomobile seats, cushioning, mattresses, and the like. Rigid foamsgenerally have a closed cell structure, where the cell walls arecontinuous and complete, and are used for used traditionally forautomobile panels and parts, building insulation and the like. Manyfoams contain both open and closed cells. It also is possible toformulate flexible foams having a closed cell structure and likewise toformulate rigid foams having an open cell structure.

A wide variety of thermoplastic and thermoset materials may be used ingenerating the foam composition of this invention including, forexample, polyurethanes; polyureas; copolymers, blends and hybrids ofpolyurethane and polyurea; olefin-based copolymer ionomer resins (forexample, Surlyn® ionomer resins and DuPont HPF® 1000 and HPF® 2000,commercially available from DuPont; Iotek® ionomers, commerciallyavailable from ExxonMobil Chemical Company; Amplify® IO ionomers ofethylene acrylic acid copolymers, commercially available from DowChemical Company; and Clarix® ionomer resins, commercially availablefrom A. Schulman Inc.); polyethylene, including, for example, lowdensity polyethylene, linear low density polyethylene, and high densitypolyethylene; polypropylene; rubber-toughened olefin polymers; acidcopolymers, for example, poly(meth)acrylic acid, which do not becomepart of an ionomeric copolymer; plastomers; flexomers;styrene/butadiene/styrene block copolymers;styrene/ethylene-butylene/styrene block copolymers; dynamicallyvulcanized elastomers; copolymers of ethylene and vinyl acetates;copolymers of ethylene and methyl acrylates; polyvinyl chloride resins;polyamides, poly(amide-ester) elastomers, and graft copolymers ofionomer and polyamide including, for example, Pebax® thermoplasticpolyether block amides, commercially available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinggood playing performance properties as discussed further below. By theterm, “hybrids of polyurethane and polyurea,” it is meant to includecopolymers and blends thereof.

Basically, polyurethane compositions contain urethane linkages formed bythe reaction of a multi-functional isocyanate containing two or more NCOgroups with a polyol having two or more hydroxyl groups (OH—OH)sometimes in the presence of a catalyst and other additives. Generally,polyurethanes can be produced in a single-step reaction (one-shot) or ina two-step reaction via a prepolymer or quasi-prepolymer. In theone-shot method, all of the components are combined at once, that is,all of the raw ingredients are added to a reaction vessel, and thereaction is allowed to take place. In the prepolymer method, an excessof polyisocyanate is first reacted with some amount of a polyol to formthe prepolymer which contains reactive NCO groups. This prepolymer isthen reacted again with a chain extender or curing agent polyol to formthe final polyurethane. Polyurea compositions, which are distinct fromthe above-described polyurethanes, also can be formed. In general,polyurea compositions contain urea linkages formed by reacting anisocyanate group (—N═C═O) with an amine group (NH or NH₂). Polyureas canbe produced in similar fashion to polyurethanes by either a one shot orprepolymer method. In forming a polyurea polymer, the polyol would besubstituted with a suitable polyamine. Hybrid compositions containingurethane and urea linkages also may be produced. For example, whenpolyurethane prepolymer is reacted with amine-terminated curing agentsduring the chain-extending step, any excess isocyanate groups in theprepolymer will react with the amine groups in the curing agent. Theresulting polyurethane-urea composition contains urethane and urealinkages and may be referred to as a hybrid. In another example, ahybrid composition may be produced when a polyurea prepolymer is reactedwith a hydroxyl-terminated curing agent. A wide variety of isocyanates,polyols, polyamines, and curing agents can be used to form thepolyurethane and polyurea compositions as discussed further below.

To prepare the foamed polyurethane, polyurea, or other polymercomposition, a foaming agent is introduced into the polymer formulation.In general, there are two types of foaming agents: physical foamingagents and chemical foaming agents.

Physical foaming agents.

These foaming agents typically are gasses that are introduced under highpressure directly into the polymer composition. Chlorofluorocarbons(CFCs) and partially halogenated chlorofluorocarbons are effective, butthese compounds are banned in many countries because of theirenvironmental side effects. Alternatively, aliphatic and cyclichydrocarbon gasses such as isobutene and pentane may be used. Inertgasses, such as carbon dioxide and nitrogen, also are suitable. Withphysical foaming agents, the isocyanate and polyol compounds react toform polyurethane linkages and the reaction generates heat. Foam cellsare generated and as the foaming agent vaporizes, the gas becomestrapped in the cells of the foam.

Chemical foaming agents.

These foaming agents typically are in the form of powder, pellets, orliquids and they are added to the composition, where they decompose orreact during heating and generate gaseous by-products (for example,nitrogen or carbon dioxide). The gas is dispersed and trapped throughoutthe composition and foams it. For example, water may be used as thefoaming agent. Air bubbles are introduced into the mixture of theisocyanate and polyol compounds and water by high-speed mixingequipment. As discussed in more detail further below, the isocyanatesreact with the water to generate carbon dioxide which fills and expandsthe cells created during the mixing process.

Preferably, a chemical foaming agent is used to prepare the foamcompositions of this invention. Chemical blowing agents may beinorganic, such as ammonium carbonate and carbonates of alkalai metals,or may be organic, such as azo and diazo compounds, such asnitrogen-based azo compounds. Suitable azo compounds include, but arenot limited to, 2,2′-azobis(2-cyanobutane),2,2′-azobis(methylbutyronitrile), azodicarbonamide, p,p′-oxybis(benzenesulfonyl hydrazide), p-toluene sulfonyl semicarbazide, p-toluenesulfonyl hydrazide. Other foaming agents include any of the Celogens®sold by Crompton Chemical Corporation, and nitroso compounds,sulfonylhydrazides, azides of organic acids and their analogs,triazines, tri- and tetrazole derivatives, sulfonyl semicarbazides, ureaderivatives, guanidine derivatives, and esters such as alkoxyboroxines.Also, foaming agents that liberate gasses as a result of chemicalinteraction between components such as mixtures of acids and metals,mixtures of organic acids and inorganic carbonates, mixtures of nitrilesand ammonium salts, and the hydrolytic decomposition of urea may beused. Water is a preferred foaming agent. When added to the polyurethaneformulation, water will react with the isocyanate groups and formcarbamic acid intermediates. The carbamic acids readily decarboxylate toform an amine and carbon dioxide. The newly formed amine can thenfurther react with other isocyanate groups to form urea linkages and thecarbon dioxide forms the bubbles to produce the foam.

During the decomposition reaction of certain chemical foaming agents,more heat and energy is released than is needed for the reaction. Oncethe decomposition has started, it continues for a relatively long timeperiod. If these foaming agents are used, longer cooling periods aregenerally required. Hydrazide and azo-based compounds often are used asexothermic foaming agents. On the other hand, endothermic foaming agentsneed energy for decomposition. Thus, the release of the gasses quicklystops after the supply of heat to the composition has been terminated.If the composition is produced using these foaming agents, shortercooling periods are needed. Bicarbonate and citric acid-based foamingagents can be used as exothermic foaming agents.

Other suitable foaming agents include expandable gas-containingmicrospheres. Exemplary microspheres consist of an acrylonitrile polymershell encapsulating a volatile gas, such as isopentane gas. This gas iscontained within the sphere as a blowing agent. In their unexpandedstate, the diameter of these hollow spheres range from 10 to 17 μm andhave a true density of 1000 to 1300 kg/m³. When heated, the gas insidethe shell increases its pressure and the thermoplastic shell softens,resulting in a dramatic increase of the volume of the microspheres.Fully expanded, the volume of the microspheres will increase more than40 times (typical diameter values would be an increase from 10 to 40μm), resulting in a true density below 30 kg/m³ (0.25 lbs/gallon).Typical expansion temperatures range from 80-190° C. (176-374° F.). Suchexpandable microspheres are commercially available as Expancel® fromExpancel of Sweden or Akzo Nobel.

Additionally, BASF polyurethane materials sold under the trade nameCellasto® and Elastocell®, microcellular polyurethanes, Elastopor® Hthat is a closed-cell polyurethane rigid foam, Elastoflex® W flexiblefoam systems, Elastoflex® E semiflexible foam systems, Elastofoam®flexible integrally-skinning systems, Elastolit® D/K/R integral rigidfoams, Elastopan® S, Elastollan® thermoplastic polyurethane elastomers(TPUs), and the like may be used in accordance with the presentinvention. Furthermore, BASF closed-cell, pre-expanded thermoplastic(TPU) polyurethane foam, available under the mark, Infinergy™ also maybe used to form the foam centers of the golf balls in accordance withthis invention. It also is believed these foam materials would be usefulin forming non-center foamed layers in a variety of golf ballconstructions. Such closed-cell, pre-expanded TPU foams are described inPrissok et al., US Patent Applications 2012/0329892; 2012/0297513; and2013/0227861; and U.S. Pat. No. 8,282,851 the disclosures of which arehereby incorporated by reference. Bayer also produces a variety ofmaterials sold as Texin® TPUs, Baytec® and Vulkollan® elastomers,Baymer® rigid foams, Baydur® integral skinning foams, Bayfit® flexiblefoams available as castable, RIM grades, sprayable, and the like thatmay be used. Additional foam materials that may be used herein includepolyisocyanurate foams and a variety of “thermoplastic” foams, which maybe cross-linked to varying extents using free-radical (for example,peroxide) or radiation cross-linking (for example, UV, IR, Gamma, EBirradiation). Also, foams may be prepared from polybutadiene,polystyrene, polyolefin (including metallocene and other single sitecatalyzed polymers), ethylene vinyl acetate (EVA), acrylate copolymers,such as EMA, EBA, Nucrel®-type acid co and terpolymers, ethylenepropylene rubber (such as EPR, EPDM, and any ethylene copolymers),styrene-butadiene, and SEBS (any Kraton-type), PVC, PVDC, CPE(chlorinated polyethylene). Epoxy foams, urea-formaldehyde foams, latexfoams and sponge, silicone foams, fluoropolymer foams and syntacticfoams (hollow sphere filled) also may be used. In particular, siliconefoams may be used.

In addition to the polymer and foaming agent, the foam composition alsomay include other ingredients such as, for example, fillers,cross-linking agents, chain extenders, surfactants, dyes and pigments,coloring agents, fluorescent agents, adsorbents, stabilizers, softeningagents, impact modifiers, antioxidants, antiozonants, and the like. Theformulations used to prepare the polyurethane foam compositions of thisinvention preferably contain a polyol, polyisocyanate, water, an amineor hydroxyl curing agent, surfactant, and a catalyst as describedfurther below.

More particularly, the foam composition this invention may be preparedfrom a composition comprising an aromatic polyurethane, which ispreferably formed by reacting an aromatic diisocyanate with a polyol.Suitable aromatic diisocyanates that may be used in accordance with thisinvention include, for example, toluene 2,4-diisocyanate (TDI), toluene2,6-diisocyanate (TDI), 4,4′-methylene diphenyl diisocyanate (MDI),2,4′-methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyldiisocyanate (PMDI), p-phenylene diisocyanate (PPDI), m-phenylenediisocyanate (PDI), naphthalene 1,5-diisocyanate (NDI), naphthalene2,4-diisocyanate (NDI), p-xylene diisocyanate (XDI), and homopolymersand copolymers and blends thereof. The aromatic isocyanates are able toreact with the hydroxyl or amine compounds and form a durable and toughpolymer having a high melting point. The resulting polyurethanegenerally has good mechanical strength and tear-resistance.

Alternatively, the foamed composition may be prepared from a compositioncomprising aliphatic polyurethane, which is preferably formed byreacting an aliphatic diisocyanate with a polyol. Suitable aliphaticdiisocyanates that may be used in accordance with this inventioninclude, for example, isophorone diisocyanate (IPDI), 1,6-hexamethylenediisocyanate (HDI), 4,4′-dicyclohexylmethane diisocyanate (“H₁₂ MDI”),meta-tetramethylxylyene diisocyanate (TMXDI), trans-cyclohexanediisocyanate (CHDI), 1,3-bis(isocyanatomethyl)cyclohexane;1,4-bis(isocyanatomethyl)cyclohexane; and homopolymers and copolymersand blends thereof. The resulting polyurethane generally has good lightand thermal stability. Preferred polyfunctional isocyanates include4,4′-methylene diphenyl diisocyanate (MDI), 2,4′-methylene diphenyldiisocyanate (MDI), and polymeric MDI having a functionality in therange of 2.0 to 3.5 and more preferably 2.2 to 2.5.

Any suitable polyol may be used to react with the polyisocyanate inaccordance with this invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG),polyethylene propylene glycol, polyoxypropylene glycol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bondsand substituted or unsubstituted aromatic and cyclic groups. Preferably,the polyol of the present invention includes PTMEG.

Chain extenders (curing agents) are added to the mixture to build-up themolecular weight of the polyurethane polymer. In general,hydroxyl-terminated curing agents, amine-terminated curing agents, andmixtures thereof are used.

A catalyst may be employed to promote the reaction between theisocyanate and polyol compounds. Suitable catalysts include, but are notlimited to, bismuth catalyst; zinc octoate; tin catalysts such asbis-butyltin dilaurate, bis-butyltin diacetate, stannous octoate; tin(II) chloride, tin (IV) chloride, bis-butyltin dimethoxide,dimethyl-bis[1-oxonedecyl)oxy]stannane, di-n-octyltin bis-isooctylmercaptoacetate; amine catalysts such as triethylenediamine,triethylamine, tributylamine, 1,4-diaza(2,2,2)bicyclooctane,tetramethylbutane diamine, bis[2-dimethylaminoethyl]ether,N,N-dimethylaminopropylamine, N,N-dimethylcyclohexylamine,N,N,N′,N′,N″-pentamethyldiethylenetriamine, diethanolamine,dimethtlethanolamine, N-[2-(dimethylamino)ethyl]-N-methylethanolamine,N-ethylmorpholine, 3-dimethylamino-N,N-dimethylpropionamide, andN,N′,N″-dimethylaminopropylhexahydrotriazine; organic acids such asoleic acid and acetic acid; delayed catalysts; and mixtures thereof.Zirconium-based catalysts such as, for example, bis(2-dimethylaminoethyl) ether; mixtures of zinc complexes and amine compounds suchas KKAT™ XK 614, available from King Industries; and amine catalystssuch as Niax™ A-2 and A-33, available from Momentive SpecialtyChemicals, Inc. are particularly preferred. The catalyst is preferablyadded in an amount sufficient to catalyze the reaction of the componentsin the reactive mixture. In one embodiment, the catalyst is present inan amount from about 0.001 percent to about 1 percent, and preferably0.1 to 0.5 percent, by weight of the composition.

In one preferred embodiment, as described above, water is used as thefoaming agent—the water reacts with the polyisocyanate compound(s) andforms carbon dioxide gas which induces foaming of the mixture. Thereaction rate of the water and polyisocyanate compounds affects howquickly the foam is formed as measured per reaction profile propertiessuch as cream time, gel time, and rise time of the foam.

Fillers.

The foam composition may contain fillers such as, for example, mineralfiller particulate. Suitable mineral filler particulates includecompounds such as zinc oxide, limestone, silica, mica, barytes,lithopone, zinc sulfide, talc, calcium carbonate, magnesium carbonate,clays, powdered metals and alloys such as bismuth, brass, bronze,cobalt, copper, iron, nickel, tungsten, aluminum, tin, precipitatedhydrated silica, fumed silica, mica, calcium metasilicate, bariumsulfate, zinc sulfide, lithopone, silicates, silicon carbide,diatomaceous earth, carbonates such as calcium or magnesium or bariumcarbonate, sulfates such as calcium or magnesium or barium sulfate.Adding fillers to the composition provides many benefits includinghelping improve the stiffness and strength of the composition. Themineral fillers tend to help decrease the size of the foam cells andincrease cell density. The mineral fillers also tend to help improve thephysical properties of the foam such as hardness, compression set, andtensile strength. More particularly, clay particulate fillers, such asGaramite® mixed mineral thixotropes and Cloisite® and Nanofil®nanoclays, commercially available from Southern Clay Products, Inc., andNanomax® and Nanomer® nanoclays, commercially available from Nanocor,Inc may be used.

Surfactants.

The foam composition also may contain surfactants to stabilize the foamand help control the foam cell size and structure. In one preferredversion, the foam composition includes silicone surfactant. In general,the silicone surfactant helps regulate the foam cell size and stabilizesthe cell walls to prevent the cells from collapsing. As discussed above,the liquid reactants react to form the foam rapidly. The “liquid” foamdevelops into solid silicone foam in a relatively short period of time.If a silicone surfactant is not added, the gas-liquid interface betweenthe liquid reactants and expanding gas bubbles may not support thestress. As a result, the cell window can crack or rupture and there canbe cell wall drainage. In turn, the foam can collapse on itself. Addinga silicone surfactant helps create a surface tension gradient along thegas-liquid interface and helps reduce cell wall drainage. The siliconesurfactant has a relatively low surface tension and thus can lower thesurface tension of the foam. It is believed the silicone surfactantorients itself the foam cell walls and lowers the surface tension tocreate the surface tension gradient. Blowing efficiency and nucleationare supported by adding the silicone surfactant and thus more bubblesare created in the system. The silicone surfactant also helps create agreater number of smaller sized foam cells and increases the closed cellcontent of the foam due to the surfactant's lower surface tension. Thus,the cell structure in the foam is maintained as the as gas is preventedfrom diffusing out through the cell walls. Along with the decrease incell size, there is a decrease in thermal conductivity. The resultingfoam material also tends to have greater compression strength andmodulus. These improved physical properties may be due to the increasein closed cell content and smaller cell size.

Properties of Polyurethane Foams

The polyurethane foam compositions of this invention have numerouschemical and physical properties making them suitable for coreassemblies in golf balls. For example, there are properties relating tothe reaction of the isocyanate and polyol components and blowing agent,particularly “cream time,” “gel time,” “rise time,” “tack-free time,”and “free-rise density.” In general, cream time refers to the timeperiod from the point of mixing the raw ingredients together to thepoint where the mixture turns cloudy in appearance or changes color andbegins to rise from its initial stable state. Normally, the cream timeof the foam compositions of this invention is within the range of about20 to about 240 seconds. In general, gel time refers to the time periodfrom the point of mixing the raw ingredients together to the point wherethe expanded foam starts polymerizing/gelling. Rise time generallyrefers to the time period from the point of mixing the raw ingredientstogether to the point where the reacted foam has reached its largestvolume or maximum height. The rise time of the foam compositions of thisinvention typically is in the range of about 60 to about 360 seconds.Tack-free time generally refers to the time it takes for the reactedfoam to lose its tackiness, and the foam compositions of this inventionnormally have a tack-free time of about 60 to about 3600 seconds.Free-rise density refers to the density of the resulting foam when it isallowed to rise unrestricted without a cover or top being placed on themold.

The density of the foam is an important property and is defined as theweight per unit volume (typically, g/cm³) and can be measured per ASTMD-1622. The hardness, stiffness, and load-bearing capacity of the foamare independent of the foam's density, although foams having a highdensity typically have high hardness and stiffness. Normally, foamshaving higher densities have higher compression strength. Surprisingly,the foam compositions used to produce the inner core of the golf ballsper this invention have a relatively low density; however, the foams arenot necessarily soft and flexible, rather, they may be relatively firm,rigid, or semi-rigid depending upon the desired golf ball properties.Tensile strength, tear-resistance, and elongation generally refer to thefoam's ability to resist breaking or tearing, and these properties canbe measured per ASTM D-1623. The durability of foams is important,because introducing fillers and other additives into the foamcomposition can increase the tendency of the foam to break or tearapart. In general, the tensile strength of the foam compositions of thisinvention is in the range of about 20 to about 1000 psi (parallel to thefoam rise) and about 50 to about 1000 psi (perpendicular to the foamrise) as measured per ASTM D-1623 at 23° C. and 50% relative humidity(RH). Meanwhile, the flex modulus of the foams of this invention isgenerally in the range of about 5 to about 45 kPa as measured per ASTMD-790, and the foams generally have a compressive modulus of 200 to50,000 psi.

In another test, compression strength is measured on an Instron machineaccording to ASTM D-1621. The foam is cut into blocks and thecompression strength is measured as the force required for compressingthe block by 10%. In general, the compressive strength of the foamcompositions of this invention is in the range of about 100 to about1800 psi (parallel and perpendicular to the foam rise) as measured perASTM D-1621 at 23° C. and 50% relative humidity (RH). The test isconducted perpendicular to the rise of the foam or parallel to the riseof the foam. The Percentage (%) of Compression Set also can be used.This is a measure of the permanent deformation of a foam sample after ithas been compressed between two metal plates under controlled time andtemperature condition (standard—22 hours at 70° C. (158° F.)). The foamis compressed to a thickness given as a percentage of its originalthickness that remained “set.” Preferably, the Compression Set of thefoam is less than ten percent (10%), that is, the foam recovers to apoint of 90% or greater of its original thickness.

The foam compositions of this invention may be prepared using differentmethods. In one preferred embodiment, the method involves preparing acastable composition comprising a reactive mixture of a polyisocyanate,polyol, water, curing agent, surfactant, and catalyst. A motorized mixercan be used to mix the starting ingredients together and form a reactiveliquid mixture. Alternatively, the ingredients can be manually mixedtogether. An exothermic reaction occurs when the ingredients are mixedtogether and this continues as the reactive mixture is dispensed intothe mold cavities (otherwise referred to as half-molds or mold cups).

Diameter and Hardness of Core and Intermediate Layer Structure

The inner core preferably has a diameter in the range of about 0.100 toabout 1.600 inches. For example, the inner core may have a diameterwithin a range of about 1.400 inches to about 1.580 inches. In anotherexample, the inner core may have a diameter within a range of about0.400 to about 1.400 inches. As far as the intermediate layer isconcerned, it preferably has a thickness in the range of about 0.100 toabout 0.750 inches. For example, the intermediate layer can have athickness of about 0.15 to about 0.40 inches.

Golf balls made in accordance with this invention can be of any size,although the USGA requires that golf balls used in competition have adiameter of at least 1.68 inches. For play outside of USGA rules, thegolf balls can be of a smaller size. Normally, golf balls aremanufactured in accordance with USGA requirements and have a diameter inthe range of about 1.68 to about 1.80 inches. There is no upper sizelimit so some golf balls, if desired, can be made having an overalldiameter greater than 1.80 inches, for example, 1.90 or 2.10, or 2.60 or3.20 inches or 3.50 inches or even greater. Preferably, the golf balldiameter is about 1.68 to 1.74 inches, more preferably about 1.68 to1.70 inches. As discussed above, the golf ball contains a cover that maybe multi-layered and also may contain intermediate layers, so thethickness levels of these layers also must be considered. In general,the dual-core structure has an overall diameter within a range having alower limit of about 1.00 or 1.20 or 1.30 or 1.40 inches and an upperlimit of about 1.55 or 1.58 or 1.60 or 1.63 or 1.65 inches. In oneembodiment, the diameter of the core sub-assembly is in the range ofabout 1.20 to about 1.60 inches. In another embodiment, the coresub-assembly has a diameter in the range of about 1.30 to about 1.58inches, and in yet another version, the core diameter is about 1.40 toabout 1.55 inches.

In general, hardness gradients are described in Bulpett et al., U.S.Pat. Nos. 7,537,529 and 7,410,429, the disclosures of which are herebyincorporated by reference. Methods for measuring the hardness of theinner core and outer core layers along with other layers in the golfball and determining the hardness gradients of the various layers aredescribed in further detail below. The core layers have positive,negative, or zero hardness gradients defined by hardness measurementsmade at the outer surface of the inner core (or outer surface of theintermediate layer) and radially inward towards the center of the innercore (or inner surface or midpoint of the intermediate layer). Thesemeasurements are made typically at 2-mm increments as described in thetest methods below. In general, the hardness gradient is determined bysubtracting the hardness value at the innermost portion of the componentbeing measured (for example, the center of the inner core or innersurface or midpoint of the intermediate layer) from the hardness valueat the outer surface of the component being measured (for example, theouter surface of the inner core or outer surface of the intermediatelayer).

Positive Hardness Gradient.

For example, if the hardness value of the outer surface of the innercore is greater than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface harder than its geometriccenter), the hardness gradient will be deemed “positive” (a largernumber minus a smaller number equals a positive number.) For example, ifthe outer surface of the inner core has a hardness of 67 Shore C and thegeometric center of the inner core has a hardness of 60 Shore C, thenthe inner core has a positive hardness gradient of 7. Likewise, if theouter surface of the intermediate layer has a greater hardness valuethan the inner surface (or midpoint) of the intermediate layer, thegiven intermediate layer will be considered to have a positive hardnessgradient.

Negative Hardness Gradient.

On the other hand, if the hardness value of the outer surface of theinner core is less than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface softer than its geometriccenter), the hardness gradient will be deemed “negative.” For example,if the outer surface of the inner core has a hardness of 68 Shore C andthe geometric center of the inner core has a hardness of 70 Shore C,then the inner core has a negative hardness gradient of 2. Likewise, ifthe outer surface of the intermediate layer has a lesser hardness valuethan the inner surface (or midpoint) of the intermediate layer, thegiven intermediate layer will be considered to have a negative hardnessgradient.

Zero Hardness Gradient.

In another example, if the hardness value of the outer surface of theinner core is substantially the same as the hardness value of the innercore's geometric center (that is, the surface of the inner core hasabout the same hardness as the geometric center), the hardness gradientwill be deemed “zero.” For example, if the outer surface of the innercore and the geometric center of the inner core each has a hardness of65 Shore C, then the inner core has a zero hardness gradient. Likewise,if the outer surface of the intermediate layer has a hardness valueapproximately the same as the inner surface (or midpoint) of theintermediate layer, the intermediate layer will be considered to have azero hardness gradient.

More particularly, the term, “positive hardness gradient” as used hereinmeans a hardness gradient of positive 1 Shore C or greater, preferably 3or 7 Shore C or greater, more preferably 10 Shore C, and even morepreferably 20 Shore C or greater. The term, “zero hardness gradient” asused herein means a hardness gradient of less than 1 Shore C and mayhave a value of zero or negative 1 to negative 10 Shore C. The term,“negative hardness gradient” as used herein means a hardness value ofless than zero, for example, negative 3, negative 5, negative 7,negative 10, negative 15, or negative 20 or negative 25. The terms,“zero hardness gradient” and “negative hardness gradient” may be usedherein interchangeably to refer to hardness gradients of negative 1 tonegative 10.

The inner core preferably has a geometric center hardness(H_(inner core center)) of about 20 Shore D or greater. For example, the(H_(inner core center)) may be in the range of about 20 to about 80Shore D and more particularly within a range having a lower limit ofabout 20 or 22 or 26 or 30 or 34 or 36 or 38 or 42 or 48 or 50 or 52Shore D and an upper limit of about 54 or 56 or 58 or 60 or 62 or 64 or68 or 70 or 74 or 76 or 78 or 80 Shore D. In another example, the centerhardness of the inner core (H_(innercore center)), as measured in ShoreC units, is preferably about 30 Shore C or greater; for example, theH_(innercore center) may have a lower limit of about 30 or 34 or 37 or40 or 44 Shore C and an upper limit of about 46 or 48 or 50 or 51 or 53or 55 or 58 or 61 or 62 or 65 or 68 or 71 or 74 or 76 or 78 or 79 or 80or 84 or 90 or 95 Shore C.

Concerning the outer surface hardness of the inner core(H_(innercore surface)), this hardness is preferably about 20 Shore D orgreater; for example, the H_(inner core surface) may fall within a rangehaving a lower limit of about 20 or 25 or 28 or 30 or 32 or 34 or 36 or40 or 42 or 48 or 50 and an upper limit of about 54 or 55 or 58 or 60 or63 or 65 or 68 or 70 or 74 or 78 or 80 or 82 or 85 Shore D. In oneversion, the outer surface hardness of the inner core(H_(inner core surface)), as measured in Shore C units, has a lowerlimit of about 30 or 32 or 35 or 38 or 40 or 42 Shore C and an upperlimit of about 45 or 48 or 50 or 53 or 56 or 58 or 60 or 62 or 65 or 68or 70 or 74 or 78 or 80 or 86 or 90 or 95 Shore C. In one version, thegeometric center hardness (H_(inner core center)) is in the range ofabout 30 Shore C to about 95 Shore C; and the outer surface hardness ofthe inner core (H_(inner core surface)) is in the range of about 30Shore C to about 95 Shore C.

On the other hand, the intermediate layer preferably has an outersurface hardness (H_(outer surface of intermed.)) of about 5 Shore D orgreater, and more preferably within a range having a lower limit ofabout 5 or 10 or 12 or 15 or 18 or 20 or 24 or 30 and an upper limit ofabout 32 or 34 or 35 or 38 or 40 or 42 or 45 or 50 or 52 or 58 or 60Shore D. The outer surface hardness of the intermediate layer(H_(outer surface of intermed.)), as measured in Shore C units,preferably has a lower limit of about 13 or 15 or 18 or 20 or 24 or 28or 30 or 33 and an upper limit of about 35 or 37 or 38 or 40 or 42 or 44or 48 or 50 or 52 or 55 or 60 Shore C.

And, the inner surface of the intermediate layer(H_(inner surface of intermed.)) or midpoint hardness of theintermediate layer (H_(midpoint of intermed.)), preferably has ahardness of about 4 Shore D or greater, and more preferably within arange having a lower limit of about 4 or 6 or 8 or 10 or 12 or 14 or 18or 20 or 24 and an upper limit of about 30 or 34 or 38 or 40 or 44 or 46or 52 Shore D. The inner surface hardness(H_(inner surface of intermed.)) or midpoint hardness(H_(midpoint of intermed.)) of the intermediate layer, as measured inShore C units, preferably has a lower limit of about 10 or 12 or 14 or17 or 20 or 22 or 24 Shore C, and an upper limit of about 28 or 30 or 35or 38 or 40 or 42 or 45 or 48 or 52 or 55 Shore C.

The inner core/intermediate layer structure also has a hardness gradientacross the entire structure. In one embodiment, the(H_(inner core center)) is in the range of about 30 to about 95 Shore C,preferably about 45 to about 75 Shore C; and the(H_(outer surface of intermediate layer)) is in the range of about 13 toabout 60 Shore C, preferably about 20 to about 50 Shore C to provide anegative hardness gradient across the sub-assembly.

In another embodiment, the H_(inner core center) is in the range ofabout 35 to about 55 Shore C and the H_(outer surface of intermed.) isin the range of about 40 to about 60 Shore C to provide a positivehardness gradient across the sub-assembly. The gradient will vary basedon several factors including, but not limited to, the dimensions of theinner core and intermediate layers.

The outer surface hardness of the foamed intermediate layer(H_(outer surface of intermed.)), as measured in Shore A units,preferably has a lower limit of about 30 or 35 or 38 or 40 or 44 or 48and an upper limit of about 55 or 57 or 60 or 62 or 64 or 68 or 70 or 72or 75 or 80 or 85 or 88 or 90 or 95 or 100. The inner surface hardness(H_(inner surface of intermed.)) or midpoint hardness(H_(midpoint of intermed.)) of the foamed intermediate layer, asmeasured in Shore A units, preferably has a lower limit of about 25 or28 or 30 or 34 or 37 or 40 or 22 or 24 or 30 or 34 or 40 Shore A, and anupper limit of about 50 or 52 or 55 or 58 or 60 or 62 or 65 or 70 or 72or 76 or 80 or 88 or 91 or 95 Shore A.

The midpoint of a layer is taken at a point equidistant from the innersurface and outer surface of the layer to be measured, most typically anouter core layer. Once one or more core layers surround a layer ofinterest, the exact midpoint may be difficult to determine, therefore,for the purposes of the present invention, the measurement of “midpoint”hardness of a layer is taken within plus or minus 1 mm of the measuredmidpoint of the layer.

Specific Gravity (Density) of Layers

In one embodiment, the specific gravity of the inner core (SG_(inner))is greater than the specific gravity of the foamed intermediate layer(SG_(intermed.)). The specific gravity (density) of the respectivelayers is an important property, because they affect the Moment ofInertia (MOI) of the ball. In one preferred embodiment, the inner corehas a relatively high specific gravity (“SG_(inner)”). For example, theinner core may have a specific gravity within a range having a lowerlimit of about 0.60 or 0.64 or 0.66 or 0.70 or 0.72 or 0.75 or 0.78 or0.80 or 0.82 or 0.85 or 0.88 or 0.90 g/cc and an upper limit of about or0.95 or 1.00 or 1.05 or 1.10 or 1.14 or 1.20 or 1.25 or 1.30 or 1.36 or1.40 or 1.42 or 1.48 or 1.50 or 1.60 or 1.66 or 1.70 1.75 or 2.00 g/cc.In a particularly preferred version, the inner core has a specificgravity of about 1.05 g/cc.

Meanwhile, the foamed intermediate layer preferably has a relatively lowspecific gravity (SG_(intermed.)). For example, the intermediate layermay have a specific gravity within a range having a lower limit of about0.20 or 0.34 or 0.28 or 0.30 or 0.34 or 0.35 or 0.40 or 0.42 or 0.44 or0.50 or 0.53 or 0.57 or 0.60 or 0.62 or 0.65 or 0.70 or 0.75 or 0.77 or0.80 g/cc and an upper limit of about 0.82 or 0.85 or 0.88 or 0.90 or0.95 or 1.00 or 1.10 or 1.15 or 1.18 or 1.25 g/cc or 1.32 or 1.35 or1.38 or 1.42 or 1.45 or 1.48 or 1.50 or 1.52 or 1.56. In a particularlypreferred version, the intermediate layer has a specific gravity ofabout 0.50 g/cc.

In a second embodiment, the specific gravity of the foamed Intermediatelayer (SG_(intermed.)) is greater than the specific gravity of the innercore (SG_(inner)). In yet another preferred embodiment, the specificgravity of the foamed intermediate layer (SG_(intermed.)) issubstantially equal to the specific gravity of the inner core(SG_(inner)).

When comparing the specific gravities of the layers, it is generallymeant by the term, “specific gravity of the inner core” (“SG_(inner)”),it is generally meant the specific gravity of the inner core as measuredat any point in the inner core layer. Likewise, by the term, “specificgravity of the intermediate layer” (“SG_(intermed)”), it is meant thespecific gravity of the intermediate layer as measured at any point inthe intermediate layer. However, it is recognized the specific gravityof the layers may vary at different particular points within therespective layers. Thus, there may be specific gravity gradients withinthe layers. For example, the midpoint region of the foamed compositioncomprising the intermediate layer may have a density in the range ofabout 0.25 to about 0.75 g/cc; while the outer skin of the foamcomposition (outer surface of the intermediate layer) may have a densityin the range of about 0.75 to about 1.35 g/cc. These specific gravitygradients within the layers are discussed further below.

In general, the specific gravities of the respective pieces of an objectaffect the Moment of Inertia (MOI) of the object. The Moment of Inertiaof a ball (or other object) about a given axis generally refers to howdifficult it is to change the ball's angular motion about that axis. Ifthe ball's mass is concentrated towards the center, less force isrequired to change its rotational rate, and the ball has a relativelylow Moment of Inertia. In such balls, the center piece (that is, theinner core) has a higher specific gravity than the outer piece (that is,the outer core layer). In such balls, most of the mass is located closeto the ball's axis of rotation and less force is needed to generatespin. Thus, the ball has a generally high spin rate as the ball leavesthe club's face after making impact. Because of the high spin rate,amateur golfers may have a difficult time controlling the ball andhitting it in a relatively straight line. Such high-spin balls tend tohave a side-spin so that when a golfer hook or slices the ball, it maydrift off-course.

Conversely, if the ball's mass is concentrated towards the outersurface, more force is required to change its rotational rate, and theball has a relatively high Moment of Inertia. In such balls, the centerpiece (that is, the inner core) has a lower specific gravity than theouter piece (that is, the outer core layer). That is, in such balls,most of the mass is located away from the ball's axis of rotation andmore force is needed to generate spin. Thus, the ball has a generallylow spin rate as the ball leaves the club's face after making impact.Because of the low spin rate, amateur golfers may have an easier timecontrolling the ball and hitting it in a relatively straight line. Theball tends to travel a greater distance which is particularly importantfor driver shots off the tee.

As described in Sullivan, U.S. Pat. No. 6,494,795 and Ladd et al., U.S.Pat. No. 7,651,415, the formula for the Moment of Inertia for a spherethrough any diameter is given in the CRC Standard Mathematical Tables,24th Edition, 1976 at 20 (hereinafter CRC reference). The term,“specific gravity” as used herein, has its ordinary and customarymeaning, that is, the ratio of the density of a substance to the densityof water at 4° C., and the density of water at this temperature is 1g/cm³.

The golf balls of this invention having the above-describedcore/intermediate layer constructions show both good resiliency and spincontrol. In the balls of this invention, the specific gravity of theinner core layer (SG_(inner)) is preferably greater than the specificgravity of the intermediate layer (SG_(intermed.)). Still, the overalldensity of the core is generally balanced. As discussed above, thenon-foamed composition used to make the inner core has a relatively highspecific gravity. However, the foamed composition used to make thesurrounding intermediate layer is slightly positioned away from thecenter of the ball. Thus, the ball does not have a relatively high orlow moment of inertia. Rather, the ball can be described as having arelative “medium moment of inertia.”

The foam cores and resulting balls also have relatively high resiliencyso the ball will reach a relatively high velocity when struck by a golfclub and travel a long distance. In particular, the inner foam cores ofthis invention preferably have a Coefficient of Restitution (COR) ofabout 0.300 or greater; more preferably about 0.400 or greater, and evenmore preferably about 0.450 or greater. The resulting balls containingthe core/intermediate layer constructions of this invention and cover ofat least one layer preferably have a COR of about 0.700 or greater, morepreferably about 0.730 or greater; and even more preferably about 0.750to 0.810 or greater. Also, the foam intermediate layers preferably havea Soft Center Deflection Index (“SCDI”) compression, as described in theTest Methods below, in the range of about 50 to about 190, and morepreferably in the range of about 60 to about 170.

Specific Gravity Gradients

There are several different ways of creating a specific gravity gradientwithin the layers, particularly the foamed intermediate layer. Thesemethods include, for example, the following: 1) The foam composition canbe treated so that it includes a fully-foamed region and a partially orcompletely-collapsed foam outer region. The density of the collapsedfoam region is greater than the density of the fully-foamed region. Heatcan be used to partially-collapse the foamed outer region and make itdenser. This method is described in further detail below. 2) Foamshaving an open cell morphology, where the cells walls are incomplete orcontain small holes can be prepared. These foams can be soaked in one ormore reactive liquids so the liquid permeates a portion of the foam andreacts to form a region of greater density. This region can be curedresulting in a layer having a density gradient. 3) Secondary blowingagents that can be activated by heat or over-molding of additionallayers also can be used to create a density gradient.

In one embodiment, the method for making the core assembly (non-foamedinner core and surrounding foamed outer core layer) comprises thefollowing steps. First, a non-foam composition is molded into an innercore structure. Secondly, a foam composition is molded into anintermediate layer structure. Then, the foamed intermediate layer isthermally or chemically-treated so as to at least partially-collapse thefoam in the outer region. In some instances, the foam in the outerregion is completely collapsed by this treatment.

Referring to FIG. 5, in one preferred embodiment, a ball sub-assembly(33) comprising an inner core (34) made from a non-foamed compositionand an intermediate layer (36) made from a foamed composition, asdescribed above, is shown. The foamed intermediate layer (36) includes amidpoint region (38) and surrounding outer surface region (40) and outersurface (42). When the intermediate layer (36) is first made, themidpoint region (38) and surrounding outer region (40) are foamed. Theouter surface (42) of the intermediate layer is generally non-foamed andis a relatively thin and dense layer. This outer surface may be referredto as the “skin” of the foamed composition (intermediate layer). In oneembodiment, the thickness of the outer skin (42) is in the range ofabout 0.001 inches (1 mil) to about 0.050 inches (50 mils) andpreferably in the range of about 0.002 to about 0.030 inches and morepreferably in the range of about 0.005 to about 0.015 inches. In oneparticular example, the thickness of the outer skin (42) can be lessthan about 0.025 inches and even less than 0.015 inches.

In a subsequent step, as described in further detail below, the foamedintermediate layer (36) is thermally or chemically-treated. For example,in one preferred embodiment, an inner cover layer is over-molded theintermediate layer. In this process, the heat used in the molding cycleactivates/decomposes the foamed outer region (40) of the intermediatelayer (36). This over-molding step causes the foamed outer region (40)of the outer core (36) to at least partially collapse. The foamed outerregion (40) becomes at least partially non-foamed as the foam collapses.The outer region (40) becomes denser (that is, less foamed). In someinstances, the foamed outer region (40) collapses completely and becomescompletely non-foamed.

Referring to FIG. 6, the intermediate layer (36) is shown with a foamedmidpoint region (38) and partially-collapsed outer region (40) and outersurface (skin) (42). A cover layer (46), which is formed by anover-molding process, surrounds the intermediate layer (36). In someinstances, the foam in the outer region (40) is completely collapsed bythis treatment. Meanwhile, the foamed state of the midpoint region (38)is maintained. The foamed geometric center, partially-collapsed outerregion, and outer skin of the outer core layer have differentmorphologies. For example, there is generally lower volume of foam cellsin the partially-collapsed outer region. A cover layer (46), which isformed by the over-molding process, surrounds the intermediate layer(36).

The cover layer (46) may be molded over the foamed outer core (36) usinga variety of molding methods that involve subjecting the core (36) toheat and pressure. For example, the cover composition (46) (preferably athermoplastic composition) may be

This heat/pressure treatment creates a non-foamed outer region (40)having different properties than the foamed midpoint region (38) of thefoamed intermediate layer (36). For example, in one preferredembodiment, the hardness of the outer region (40) is greater than thehardness of the midpoint region (38) to create a positive hardnessgradient across the outer core layer (36). These hardness gradients arediscussed in further detail below. The specific gravity (or density) ofthe outer region (40) also may be greater than the specific gravity ofthe midpoint region (38). That is, there can be specific gravitygradients within the foamed intermediate layer.

For example, the foamed intermediate layer (36) may have an outersurface specific gravity (SG_(intermediate layer surface)) and amidpoint specific gravity (SG_(intermediate layer midpoint)), whereinthe SG_(intermediate layer surface) is greater than theSG_(intermediate layer midpoint). For example, the midpoint specificgravity can be within a range having a lower limit of about 0.20 or 0.24or 0.28 or 0.30 or 0.34 or 0.35 or 0.40 or 0.42 or 0.44 or 0.50 or 0.53or 0.57 or 0.60 or 0.62 or 0.65 or 0.70 or 0.75 or 0.77 or 0.80 and ahigher limit of about 0.82 or 0.85 or 0.88 or 0.90 or 0.95 or 1.00 or1.10 or 1.15 or 1.18 or 1.25 g/cc or 1.32 or 1.35 or 1.38 or 1.42 or1.45 or 1.48 or 1.50 or 1.52 or 1.57 or 1.60. The foamed intermediatealso has a specific gravity in the outer region(SG_(intermediate layer outer region)) and outer surface(SG_(intermediate layer surface)) as discussed above. For example, thespecific gravity of the outer region and/or outer surface can be withina range having a lower limit of 0.21 or 0.35 or 0.29 or 0.31 or 0.35 or0.36 or 0.41 or 0.43 or 0.45 or 0.51 or 0.54 or 0.58 or 0.61 or 0.63 or0.66 or 0.71 or 0.76 or 0.78 or 0.81 g/cc and a higher limit of about0.83 or 0.86 or 0.89 or 0.91 or 0.96 or 1.01 or 1.11 or 1.16 or 1.19 or1.26 g/cc or 1.33 or 1.36 or 1.39 or 1.43 or 1.46 or 1.49 or 1.51 or1.53 or 1.58 or 1.61.

In one preferred embodiment, the SG_(intermediate layer surface) isgreater than the SG intermediate layer outer region and theSG_(intermediate layer outer region) is greater than theSG_(intermediate layer midpoint). Thus, in one version, theSG_(intermediate layer surface)>SG_(intermediate layer outer region)>SG_(intermediate layer midpoint)by at least 0.01, more preferably by at least 0.05, and most preferablyby at least 0.1. In another preferred version, theSG_(intermediate layer) surface is greater than or equal toSG_(intermediate layer outer region) and is greater than theSG_(intermediate layer midpoint) by at least 0.01, more preferably 0.05,and most preferably 0.1.

In an alternative method, a chemical-treatment may also be used to forman outer region of greater density in the intermediate layer (36). Forexample, the foamed sphere may be exposed to a solvent that partiallydissolves or softens the outer portion of the sphere in order to causeit to collapse slightly. It is also possible to treat the foamed layerwith a reactive mixture such as polyurethane, polyurea, epoxy, or otherreactive polymer system. The liquid, non-reacted mixture can fill thevoids of the outer region (40) of the foamed sphere and react to form asolid material. In this manner, the density of the outer region (40) ofthe foamed sphere can be increased.

As discussed above, the core of the golf ball of this inventionpreferably has a dual-layered construction comprising inner and outercore layers. The USGA has established a maximum weight of 45.93 g (1.62ounces) for golf balls. For play outside of USGA rules, the golf ballscan be heavier. Since the golf ball contains a cover and also maycontain intermediate layers, the weight of these layers also must beconsidered. In one preferred embodiment, the weight of the dual-layeredcore is in the range of about 28 to about 42 grams.

Golf balls made in accordance with this invention can be of any size,although the USGA requires that golf balls used in competition have adiameter of at least 1.68 inches. For play outside of USGA rules, thegolf balls can be of a smaller size. Normally, golf balls aremanufactured in accordance with USGA requirements and have a diameter inthe range of about 1.68 to about 1.80 inches. There is no upper sizelimit so some golf balls, if desired, can be made having an overalldiameter greater than 1.80 inches, for example, 1.90 or 2.10, or 2.60 or3.20 inches or 3.50 inches or even greater. Preferably, the golf balldiameter is about 1.68 to 1.74 inches, more preferably about 1.68 to1.70 inches. In accordance with the present invention, the weight,diameter, and thickness of the core and cover layers may be adjusted, asneeded, so the ball meets USGA specifications of a maximum weight of1.62 ounces and a minimum diameter of at least 1.68 inches.

In yet other embodiments of this invention, the above-describedcompositions can be used to make golf balls having reduced distancewhile performing similar to traditional high performance balls in otherways. That is, in these embodiments, the golf ball has high playingperformance properties such as flight trajectory, spin rate, and feel,except the ball plays a shorter distance than traditional highperformance balls.

For example, in one preferred embodiment, golf ball constructions asdescribed in Sullivan et al., U.S. Pat. No. 8,152,656 (the '656 patent),the disclosure of which is hereby incorporated by reference, can bemade. Such a ball preferably has a weight from 1.30 to 1.620 ounces, adiameter from 1.670 to 1.800 inches, and a maximum Coefficient ofRestitution (CoR) from about 0.500 to about 0.790 as measured at 125ft/sec incoming ball velocity. More preferably the ball has a weight offrom about 1.50 ounces to 1.60 ounces, a diameter of 1.680 to 1.720,inches, and a CoR of from about 0.625 to 0.775 as measured at 125 ft/secincoming ball velocity. The ball has a drag to weight ratio of greaterthan 2.4 at a Reynolds number of about 207,000 and a spin ratio of about0.095.

The '656 patent also describes the reduced distance golf ball as havinga relatively high coefficient of drag (C_(D)). In one embodiment, theC_(D) is greater than 0.26 at a Reynolds number of 150000 and a spinrate of 3000 RPM, and greater than 0.29 at a Reynolds number of 120000and a spin rate of 3000 RPM. Further, golf balls prepared according tothe present invention may have a relatively high coefficient of lift(C_(L)). In one embodiment, the C_(L) is greater than 0.21 at a Reynoldsnumber of 150000 and a spin rate of 3000 RPM, and greater than 0.23 at aReynolds number of 120000 and a spin rate of 3000 RPM.

In one embodiment, the golf ball has reduced flight distance whileretaining the appearance of a normal trajectory that can be defined bytwo non-dimensional parameters that account for the lift, drag, size andweight of the ball. The coefficients are defined in the followingEquations: i) C_(D/W)=F_(D/W), and ii) C_(L/W)=F_(L/W).

A reduction in flight distance is attainable when a golf ball's size,weight, dimple pattern and dimple profiles are selected to satisfyspecific C_(D/W) and C_(L/W) criteria at specified combinations ofReynolds number and spin ratios (or spin rate), and the only otherremaining variable is the COR. The size of the golf ball affects thelift and drag of the ball, since these forces are directly proportionalto the surface area of the ball. The weight of the ball makes up thedenominator of coefficients C_(D/W) and C_(L/W). Dimple patterns, forexample, percentage of dimple coverage and geodesic patterns, canincrease or decrease aerodynamic efficiency. Dimple profiles, e.g., edgeangle, entry angle and shape (circular, polygonal), can increase ordecrease the lift and/or drag experienced by the ball. According to thepresent invention, these factors can be selected or combined to yielddesired C_(D/W) and/or C_(L/W) for a reduced distance golf ball thatretains the appearance of a high performance trajectory.

Cover Structure

The golf ball sub-assemblies of this invention may be enclosed with oneor more cover layers. The golf ball sub-assembly includes the corestructure and one or more intermediate (mantle) layers disposed aboutthe core. In one version, the golf ball includes a multi-layered covercomprising inner and outer cover layers. The inner cover layer ispreferably formed from a composition comprising an ionomer or a blend oftwo or more ionomers that helps impart hardness to the ball.

Suitable ionomer compositions include partially-neutralized ionomers andhighly-neutralized ionomers (HNPs), including ionomers formed fromblends of two or more partially-neutralized ionomers, blends of two ormore highly-neutralized ionomers, and blends of one or morepartially-neutralized ionomers with one or more highly-neutralizedionomers. For purposes of the present disclosure, “HNP” refers to anacid copolymer after at least 70% of all acid groups present in thecomposition are neutralized.

Preferred ionomers are salts of O/X- and O/X/Y-type acid copolymers,wherein O is an α-olefin, X is a C₃-C₈ α,β-ethylenically unsaturatedcarboxylic acid, and Y is a softening monomer. O is preferably selectedfrom ethylene and propylene. X is preferably selected from methacrylicacid, acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably selected from (meth) acrylate and alkyl (meth) acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth) acrylate, isobutyl (meth) acrylate,methyl (meth) acrylate, and ethyl (meth) acrylate.

Preferred O/X and O/X/Y-type copolymers include, without limitation,ethylene acid copolymers, such as ethylene/(meth)acrylic acid,ethylene/(meth)acrylic acid/maleic anhydride, ethylene/(meth)acrylicacid/maleic acid mono-ester, ethylene/maleic acid, ethylene/maleic acidmono-ester, ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/iso-butyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike. The term, “copolymer,” as used herein, includes polymers havingtwo types of monomers, those having three types of monomers, and thosehaving more than three types of monomers. Preferred c, (3-ethylenicallyunsaturated mono- or dicarboxylic acids are (meth) acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconicacid. (Meth) acrylic acid is most preferred. As used herein, “(meth)acrylic acid” means methacrylic acid and/or acrylic acid. Likewise,“(meth) acrylate” means methacrylate and/or acrylate.

In a particularly preferred version, highly neutralized E/X- andE/X/Y-type acid copolymers, wherein E is ethylene, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid, and Y is a softeningmonomer are used. X is preferably selected from methacrylic acid,acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably an acrylate selected from alkyl acrylates and aryl acrylatesand preferably selected from (meth) acrylate and alkyl (meth) acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth) acrylate, isobutyl (meth) acrylate,methyl (meth) acrylate, and ethyl (meth) acrylate. Preferred E/X/Y-typecopolymers are those wherein X is (meth) acrylic acid and/or Y isselected from (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth)acrylate, methyl (meth) acrylate, and ethyl (meth) acrylate. Morepreferred E/X/Y-type copolymers are ethylene/(meth) acrylic acid/n-butylacrylate, ethylene/(meth) acrylic acid/methyl acrylate, andethylene/(meth) acrylic acid/ethyl acrylate.

The amount of ethylene in the acid copolymer is typically at least 15wt. %, preferably at least 25 wt. %, more preferably least 40 wt. %, andeven more preferably at least 60 wt. %, based on total weight of thecopolymer. The amount of C₃ to C₈ α, β-ethylenically unsaturated mono-or dicarboxylic acid in the acid copolymer is typically from 1 wt. % to35 wt. %, preferably from 5 wt. % to 30 wt. %, more preferably from 5wt. % to 25 wt. %, and even more preferably from 5 wt. % to 20 wt. %,based on total weight of the copolymer. The amount of optional softeningcomonomer in the acid copolymer is typically from 0 wt. % to 50 wt. %,preferably from 5 wt. % to 40 wt. %, more preferably from 10 wt. % to 35wt. %, and even more preferably from 20 wt. % to 30 wt. %, based ontotal weight of the copolymer. “Low acid” and “high acid” ionomericpolymers, as well as blends of such ionomers, may be used. In general,low acid ionomers are considered to be those containing 16 wt. % or lessof acid moieties, whereas high acid ionomers are considered to be thosecontaining greater than 16 wt. % of acid moieties.

The various O/X, E/X, O/X/Y, and E/X/Y-type copolymers are at leastpartially neutralized with a cation source, optionally in the presenceof a high molecular weight organic acid, such as those disclosed inRajagopalan et al., U.S. Pat. No. 6,756,436, the entire disclosure ofwhich is hereby incorporated herein by reference. The acid copolymer canbe reacted with the optional high molecular weight organic acid and thecation source simultaneously, or prior to the addition of the cationsource. Suitable cation sources include, but are not limited to, metalion sources, such as compounds of alkali metals, alkaline earth metals,transition metals, and rare earth elements; ammonium salts and monoaminesalts; and combinations thereof. Preferred cation sources are compoundsof magnesium, sodium, potassium, cesium, calcium, barium, manganese,copper, zinc, lead, tin, aluminum, nickel, chromium, lithium, and rareearth metals. The amount of cation used in the composition is readilydetermined based on desired level of neutralization. As discussed above,for HNP compositions, the acid groups are neutralized to 70% or greater,preferably 70 to 100%, more preferably 90 to 100%. In one embodiment, anexcess amount of neutralizing agent, that is, an amount greater than thestoichiometric amount needed to neutralize the acid groups, may be used.That is, the acid groups may be neutralized to 100% or greater, forexample 110% or 120% or greater. In other embodiments,partially-neutralized compositions are prepared, wherein 10% or greater,normally 30% or greater of the acid groups are neutralized. Whenaluminum is used as the cation source, it is preferably used at lowlevels with another cation such as zinc, sodium, or lithium, sincealuminum has a dramatic effect on melt flow reduction and cannot be usedalone at high levels. For example, aluminum is used to neutralize about10% of the acid groups and sodium is added to neutralize an additional90% of the acid groups.

Ionic plasticizers such as organic acids or salts of organic acids,particularly fatty acids, may be added to the ionomer resin. Such ionicplasticizers are used to make conventional ionomer composition moreprocessable as described in the above-mentioned U.S. Pat. No. 6,756,436.In the present invention such ionic plasticizers are optional. In onepreferred embodiment, a thermoplastic ionomer composition is made byneutralizing about 70 wt % or more of the acid groups without the use ofany ionic plasticizer. On the other hand, in some instances, it may bedesirable to add a small amount of ionic plasticizer, provided that itdoes not adversely affect the heat-resistance properties of thecomposition. For example, the ionic plasticizer may be added in anamount of about 10 to about 60 weight percent (wt. %) of thecomposition, more preferably 30 to 55 wt. %.

The organic acids may be aliphatic, mono- or multi-functional(saturated, unsaturated, or multi-unsaturated) organic acids. Salts ofthese organic acids may also be employed. Suitable fatty acid saltsinclude, for example, metal stearates, laureates, oleates, palmitates,pelargonates, and the like. For example, fatty acid salts such as zincstearate, calcium stearate, magnesium stearate, barium stearate, and thelike can be used. The salts of fatty acids are generally fatty acidsneutralized with metal ions. The metal cation salts provide the cationscapable of neutralizing (at varying levels) the carboxylic acid groupsof the fatty acids. Examples include the sulfate, carbonate, acetate andhydroxide salts of metals such as barium, lithium, sodium, zinc,bismuth, chromium, cobalt, copper, potassium, strontium, titanium,tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin, orcalcium, and blends thereof. It is preferred the organic acids and saltsbe relatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending).

In a particular embodiment, the inner cover layer is formed from acomposition comprising a high acid ionomer. A particularly suitable highacid ionomer is Surlyn 8150® (DuPont). Surlyn 8150® is a copolymer ofethylene and methacrylic acid, having an acid content of 19 wt %, whichis 45% neutralized with sodium. In another particular embodiment, theinner cover layer is formed from a composition comprising a high acidionomer and a maleic anhydride-grafted non-ionomeric polymer. Aparticularly suitable maleic anhydride-grafted polymer is Fusabond 525D®(DuPont). Fusabond 525D® is a maleic anhydride-grafted,metallocene-catalyzed ethylene-butene copolymer having about 0.9 wt %maleic anhydride grafted onto the copolymer. A particularly preferredblend of high acid ionomer and maleic anhydride-grafted polymer is an 84wt %/16 wt % blend of Surlyn 8150® and Fusabond 525D®. Blends of highacid ionomers with maleic anhydride-grafted polymers are furtherdisclosed, for example, in U.S. Pat. Nos. 6,992,135 and 6,677,401, theentire disclosures of which are hereby incorporated herein by reference.

The inner cover layer also may be formed from a composition comprising a50/45/5 blend of Surlyn® 8940/Surlyn® 9650/Nucrel® 960, and, in aparticularly preferred embodiment, the composition has a materialhardness of from 80 to 85 Shore C. In yet another version, the innercover layer is formed from a composition comprising a 50/25/25 blend ofSurlyn® 8940/Surlyn® 9650/Surlyn® 9910, preferably having a materialhardness of about 90 Shore C. The inner cover layer also may be formedfrom a composition comprising a 50/50 blend of Surlyn® 8940/Surlyn®9650, preferably having a material hardness of about 86 Shore C. Acomposition comprising a 50/50 blend of Surlyn® 8940 and Surlyn® 7940also may be used. Surlyn® 8940 is an E/MAA copolymer in which the MAAacid groups have been partially neutralized with sodium ions. Surlyn®9650 and Surlyn® 9910 are two different grades of E/MAA copolymer inwhich the MAA acid groups have been partially neutralized with zincions. Nucrel® 960 is an E/MAA copolymer resin nominally made with 15 wt% methacrylic acid.

A wide variety of materials may be used for forming the outer coverincluding, for example, polyurethanes; polyureas; copolymers, blends andhybrids of polyurethane and polyurea; olefin-based copolymer ionomerresins (for example, Surlyn® ionomer resins and DuPont HPF® 1000 andHPF® 2000, commercially available from DuPont; Iotek ionomers,commercially available from ExxonMobil Chemical Company; Amplify® IOionomers of ethylene acrylic acid copolymers, commercially availablefrom The Dow Chemical Company; and Clarix® ionomer resins, commerciallyavailable from A. Schulman Inc.); polyethylene, including, for example,low density polyethylene, linear low density polyethylene, and highdensity polyethylene; polypropylene; rubber-toughened olefin polymers;acid copolymers, for example, poly(meth)acrylic acid, which do notbecome part of an ionomeric copolymer; plastomers; flexomers;styrene/butadiene/styrene block copolymers;styrene/ethylene-butylene/styrene block copolymers; dynamicallyvulcanized elastomers; copolymers of ethylene and vinyl acetates;copolymers of ethylene and methyl acrylates; polyvinyl chloride resins;polyamides, poly(amide-ester) elastomers, and graft copolymers ofionomer and polyamide including, for example, Pebax® thermoplasticpolyether block amides, commercially available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinghigh resiliency and a soft feel. By the term, “hybrids of polyurethaneand polyurea,” it is meant to include copolymers and blends thereof.

Polyurethanes, polyureas, and blends, copolymers, and hybrids ofpolyurethane/polyurea are also particularly suitable for forming coverlayers. When used as cover layer materials, polyurethanes and polyureascan be thermoset or thermoplastic. Thermoset materials can be formedinto golf ball layers by conventional casting or reaction injectionmolding techniques. Thermoplastic materials can be formed into golf balllayers by conventional compression or injection molding techniques.

The inner cover layer preferably has a material hardness within a rangehaving a lower limit of 70 or 75 or 80 or 82 Shore C and an upper limitof 85 or 86 or 90 or 92 Shore C. The thickness of the inner cover layeris preferably within a range having a lower limit of 0.010 or 0.015 or0.020 or 0.030 inches and an upper limit of 0.035 or 0.045 or 0.080 or0.120 inches. The outer cover layer preferably has a material hardnessof 85 Shore C or less. The thickness of the outer cover layer ispreferably within a range having a lower limit of 0.010 or 0.015 or0.025 inches and an upper limit of 0.035 or 0.040 or 0.055 or 0.080inches. Methods for measuring hardness of the layers in the golf ballare described in further detail below.

As discussed above, the core/intermediate layer structure of thisinvention may be enclosed with one or more cover layers. In oneembodiment, a multi-layered cover comprising inner and outer coverlayers is formed, where the inner cover layer has a thickness of about0.01 inches to about 0.06 inches, more preferably about 0.015 inches toabout 0.040 inches, and most preferably about 0.02 inches to about 0.035inches. In this version, the inner cover layer is formed from apartially- or fully-neutralized ionomer having a Shore D hardness ofgreater than about 55, more preferably greater than about 60, and mostpreferably greater than about 65. The outer cover layer, in thisembodiment, preferably has a thickness of about 0.015 inches to about0.055 inches, more preferably about 0.02 inches to about 0.04 inches,and most preferably about 0.025 inches to about 0.035 inches, with ahardness of about Shore D 80 or less, more preferably 70 or less, andmost preferably about 60 or less. The inner cover layer is harder thanthe outer cover layer in this version. A preferred outer cover layer isa castable or reaction injection molded polyurethane, polyurea orcopolymer, blend, or hybrid thereof having a Shore D hardness of about40 to about 50. In another multi-layer cover, dual-core embodiment, theouter cover and inner cover layer materials and thickness are the samebut, the hardness range is reversed, that is, the outer cover layer isharder than the inner cover layer. For this harder outer cover/softerinner cover embodiment, the ionomer resins described above wouldpreferably be used as outer cover material.

Golf Ball Construction

The solid cores for the golf balls of this invention may be made usingany suitable conventional technique such as, for example, compression orinjection molding. In some emboidments, the inner core is formed bycompression molding a slug of the uncured or lightly cured polybutadienerubber material into a substantially spherical structure. The outer corelayer, which surround the inner core, are formed by molding compositionsover the inner core. Compression or injection molding techniques may beused. Then, the intermediate (mantle) and/or cover layers are applied.Prior to this step, the core structure may be surface-treated toincrease the adhesion between its outer surface and the next layer thatwill be applied over the core. Such surface-treatment may includemechanically or chemically-abrading the outer surface of the core. Forexample, the core may be subjected to corona-discharge,plasma-treatment, silane-dipping, or other treatment methods known tothose in the art.

The intermediate and cover layers are formed over the ball subassembly(core structure) using a suitable technique such as, for example,compression-molding, flip-molding, injection-molding, retractable pininjection-molding, reaction injection-molding, liquid injection-molding,casting, spraying, powder-coating, vacuum-forming, flow-coating,dipping, spin-coating, and the like. Preferably, each cover layer isseparately formed over the ball subassembly. For example, an ethyleneacid copolymer ionomer composition may be injection-molded to producehalf-shells. Alternatively, the ionomer composition can be placed into acompression mold and molded under sufficient pressure, temperature, andtime to produce the hemispherical shells. The smooth-surfacedhemispherical shells are then placed around the ball subassembly in acompression mold. Under sufficient heating and pressure, the shells fusetogether to form an inner cover layer that surrounds the subassembly. Inanother method, the ionomer composition is injection-molded directlyonto the core using retractable pin injection molding. An outer coverlayer comprising a polyurethane or polyurea composition may be formed byusing a casting process.

For example, in one version of the casting process, a liquid mixture ofreactive polyurethane prepolymer and chain-extender (curing agent) ispoured into lower and upper mold cavities. Then, the golf ballsubassembly is lowered at a controlled speed into the reactive mixture.Ball suction cups can hold the ball subassembly in place via reducedpressure or partial vacuum. After sufficient gelling of the reactivemixture (typically about 4 to about 12 seconds), the vacuum is removedand the intermediate ball is released into the mold cavity. Then, theupper mold cavity is mated with the lower mold cavity under sufficientpressure and heat. An exothermic reaction occurs when the polyurethaneprepolymer and chain extender are mixed and this continues until thecover material encapsulates and solidifies around the ball subassembly.Finally, the molded balls are cooled in the mold and removed when themolded cover is hard enough so that it can be handled withoutdeformation.

In one such casting process, a polyurethane prepolymer and curing agentare mixed in a motorized mixer inside of a mixing head by meteringamounts of the curative and prepolymer through the feed lines. A moldhaving upper and lower hemispherical-shaped mold cavities and withinterior dimple patterns is used. Each mold cavity has an arcuate innersurface defining an inverted dimple pattern. The upper and lower moldcavities can be preheated and filled with the reactive polyurethane andcuring agent mixture. After the reactive mixture has resided in thelower mold cavities for a sufficient time period, typically about 40 toabout 100 seconds, the golf ball core/inner cover assembly can belowered at a controlled speed into the reacting mixture. Ball cups canhold the assemblies by applying reduced pressure (or partial vacuum).After sufficient gelling (typically about 4 to about 12 seconds), thevacuum can be removed and the assembly can be released. Then, the upperhalf-molds can be mated with the lower half-molds. An exothermicreaction occurs when the polyurethane prepolymer and curing agent aremixed and this continues until the material solidifies around thesubassembly. The molded balls can then be cooled in the mold and removedwhen the molded cover layer is hard enough to be handled withoutdeforming. This molding technique is described in the patent literatureincluding Hebert et al., U.S. Pat. No. 6,132,324, Wu, U.S. Pat. No.5,334,673, and Brown et al., U.S. Pat. No. 5,006,297, the disclosures ofwhich are hereby incorporated by reference.

As discussed above, the lower and upper mold cavities have interiordimple cavity details. When the mold cavities are mated together, theydefine an interior spherical cavity that forms the cover for the ball.The cover material encapsulates the inner ball subassembly to form aunitary, one-piece cover structure. Furthermore, the cover materialconforms to the interior geometry of the mold cavities to form a dimplepattern on the surface of the ball. The mold cavities may have anysuitable dimple arrangement such as, for example, icosahedral,octahedral, cube-octahedral, dipyramid, and the like. In addition, thedimples may be circular, oval, triangular, square, pentagonal,hexagonal, heptagonal, octagonal, and the like.

After the golf balls have been removed from the mold, they may besubjected to finishing steps such as flash-trimming, surface-treatment,marking, coating, and the like using techniques known in the art. Forexample, in traditional white-colored golf balls, the white-pigmentedcover may be surface-treated using a suitable method such as, forexample, corona, plasma, or ultraviolet (UV) light-treatment. Then,indicia such as trademarks, symbols, logos, letters, and the like may beprinted on the ball's cover using pad-printing, ink-jet printing,dye-sublimation, or other suitable printing methods. Clear surfacecoatings (for example, primer and top-coats), which may contain afluorescent whitening agent, are applied to the cover. The resultinggolf ball has a glossy and durable surface finish. In FIG. 4, a finishedgolf ball (30) having an outer cover with a dimpled surface (32) isshown.

In another finishing process, the golf balls are painted with one ormore paint coatings. For example, white primer paint may be appliedfirst to the surface of the ball and then a white top-coat of paint maybe applied over the primer. Of course, the golf ball may be painted withother colors, for example, red, blue, orange, and yellow. As notedabove, markings such as trademarks and logos may be applied to thepainted cover of the golf ball. Finally, a clear surface coating may beapplied to the cover to provide a shiny appearance and protect any logosand other markings printed on the ball.

Different core and ball constructions can be made per this invention asshown in FIGS. 1-6 discussed above. Such golf ball designs include, forexample, three-piece, four-piece, five-piece, and six-piece designs. Itshould be understood that the core constructions and golf balls shown inFIGS. 1-6 are for illustrative purposes only and are not meant to berestrictive. Other core constructions and golf balls can be made inaccordance with this invention.

Cores Having Three Layers

For example, multi-layered cores having an inner core, intermediate corelayer, and outer core layer, wherein the intermediate core layer isdisposed between the intermediate and outer core layers may be preparedin accordance with this invention. More particularly, as discussedabove, the inner core may be constructed from a non-foamed thermoset orthermoplastic material, preferably polybutadiene rubber as discussedabove. Meanwhile, the intermediate and outer core layers may be formedfrom foamed compositions, preferably foamed polyurethane as discussedabove. In another embodiment, the inner core layer is formed from a anon-foamed thermoset or thermoplastic composition; the intermediate corelayer is formed from a foamed composition; and the outer core layer isformed from a non-foamed thermoset or thermoplastic composition. Thespecific gravity of the core layer(s) comprising the foam composition ispreferably less than the specific gravity of the core layer(s)comprising the non-foamed composition(s).

Where more than one foam layer is used in a single golf ball, therespective foamed chemical compositions may be the same or different,and the compositions may have the same or different hardness or specificgravity levels. For example, a golf ball may contain a three-layeredcore having a non-foamed polybutadiene rubber center; a polyurethanefoam intermediate core layer; and an outer core layer comprising afoamed highly-neutralized ionomer (HNP) composition.

Test Methods

Hardness.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within 0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located 180°apart, or 90° apart, respectively, and then averaged. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder, and thus also parallel to theproperly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball subassembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements. The digital durometer must beattached to, and its foot made parallel to, the base of an automaticstand. The weight on the durometer and attack rate conforms to ASTMD-2240.

In certain embodiments, a point or plurality of points measured alongthe “positive” or “negative” gradients may be above or below a line fitthrough the gradient and its outermost and innermost hardness values. Inan alternative preferred embodiment, the hardest point along aparticular steep “positive” or “negative” gradient may be higher thanthe value at the innermost portion of the inner core (the geometriccenter) or outer core layer (the inner surface)—as long as the outermostpoint (i.e., the outer surface of the inner core) is greater than (for“positive”) or lower than (for “negative”) the innermost point (i.e.,the geometric center of the inner core or the inner surface of the outercore layer), such that the “positive” and “negative” gradients remainintact.

As discussed above, the direction of the hardness gradient of a golfball layer is defined by the difference in hardness measurements takenat the outer and inner surfaces of a particular layer. The centerhardness of an inner core and hardness of the outer surface of an innercore in a single-core ball or outer core layer are readily determinedaccording to the test procedures provided above. The outer surface ofthe inner core layer (or other optional intermediate core layers) in adual-core ball are also readily determined according to the proceduresgiven herein for measuring the outer surface hardness of a golf balllayer, if the measurement is made prior to surrounding the layer with anadditional core layer. Once an additional core layer surrounds a layerof interest, the hardness of the inner and outer surfaces of any inneror intermediate layers can be difficult to determine. Therefore, forpurposes of the present invention, when the hardness of the inner orouter surface of a core layer is needed after the inner layer has beensurrounded with another core layer, the test procedure described abovefor measuring a point located 1 mm from an interface is used. Likewise,the midpoint of a core layer is taken at a point equidistant from theinner surface and outer surface of the layer to be measured, mosttypically an outer core layer. It is recognized that when one or morecore layers surround a layer of interest, the exact midpoint may bedifficult to determine, therefore, for the purposes of the presentinvention, the measurement of “midpoint” hardness of a layer is takenwithin plus or minus 1 mm of the measured midpoint of the layer.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and “hardness as measured directly on a golfball.” For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (or other sphericalsurface) typically results in a different hardness value. The differencein “surface hardness” and “material hardness” values is due to severalfactors including, but not limited to, ball construction (that is, coretype, number of cores and/or cover layers, and the like); ball (orsphere) diameter; and the material composition of adjacent layers. Italso should be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore A, Shore Cor Shore D hardness) was measured according to the test method ASTMD-2240.

Compression.

As disclosed in Jeff Dalton's Compression by Any Other Name, Science andGolf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) (“J. Dalton”), several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, compression refers to Soft Center Deflection Index (“SCDI”).The SCDI is a program change for the Dynamic Compression Machine (“DCM”)that allows determination of the pounds required to deflect a core 10%of its diameter. The DCM is an apparatus that applies a load to a coreor ball and measures the number of inches the core or ball is deflectedat measured loads. A crude load/deflection curve is generated that isfit to the Atti compression scale that results in a number beinggenerated that represents an Atti compression. The DCM does this via aload cell attached to the bottom of a hydraulic cylinder that istriggered pneumatically at a fixed rate (typically about 1.0 ft/s)towards a stationary core. Attached to the cylinder is an LVDT thatmeasures the distance the cylinder travels during the testing timeframe.A software-based logarithmic algorithm ensures that measurements are nottaken until at least five successive increases in load are detectedduring the initial phase of the test. The SCDI is a slight variation ofthis set up. The hardware is the same, but the software and output haschanged. With the SCDI, the interest is in the pounds of force requiredto deflect a core x amount of inches. That amount of deflection is 10%percent of the core diameter. The DCM is triggered, the cylinderdeflects the core by 10% of its diameter, and the DCM reports back thepounds of force required (as measured from the attached load cell) todeflect the core by that amount. The value displayed is a single numberin units of pounds.

Drop Rebound.

By “drop rebound,” it is meant the number of inches a sphere willrebound when dropped from a height of 72 inches in this case, measuringfrom the bottom of the sphere. A scale, in inches is mounted directlybehind the path of the dropped sphere and the sphere is dropped onto aheavy, hard base such as a slab of marble or granite (typically about 1ft wide by 1 ft high by 1 ft deep). The test is carried out at about72-75° F. and about 50% RH

Coefficient of Restitution (“COR”).

The COR is determined according to a known procedure, wherein a golfball or golf ball subassembly (for example, a golf ball core) is firedfrom an air cannon at two given velocities and a velocity of 125 ft/s isused for the calculations. Ballistic light screens are located betweenthe air cannon and steel plate at a fixed distance to measure ballvelocity. As the ball travels toward the steel plate, it activates eachlight screen and the ball's time period at each light screen ismeasured. This provides an incoming transit time period which isinversely proportional to the ball's incoming velocity. The ball makesimpact with the steel plate and rebounds so it passes again through thelight screens. As the rebounding ball activates each light screen, theball's time period at each screen is measured. This provides an outgoingtransit time period which is inversely proportional to the ball'soutgoing velocity. The COR is then calculated as the ratio of the ball'soutgoing transit time period to the ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

Density.

The density refers to the weight per unit volume (typically, g/cm³) ofthe material and can be measured per ASTM D-1622.

The present invention is illustrated further by the following Examples,but these Examples should not be construed as limiting the scope of theinvention.

EXAMPLES

In the following Examples, different compositions were used to preparesample golf balls using the above-described molding methods. Thedifferent compositions and properties of the golf ball constructions aredescribed in the Tables below.

Example A (Comparative)

A polybutadiene rubber composition was molded into a spherical corehaving a diameter of 1.530 inches. Then, an ethylene acid copolymerionomer composition (Surlyn™, available from DuPont) was molded over therubber core. The resulting intermediate ball (core and intermediatelayer) had a diameter of 1.620 inches. Finally, an ethylene acidcopolymer ionomer composition was molded over the intermediate ball toform a finished ball having a diameter of 1.680 inches.

Example 1

The same polybutadiene rubber composition used in Example A was moldedinto a spherical core having a diameter of 1.530 inches. Then, a foamedpolyurethane composition having the formulation described in Table Ibelow was molded over the rubber core. The resulting intermediate ball(core and intermediate layer) had a diameter of 1.620 inches.

TABLE I Foamed Polyurethane Composition Ingredient Weight Percent 4,4Methylene Diphenyl Diisocyanate (MDI) 14.65% Polyetratmethylene etherglycol (PTMEG 2000) 34.92% *Mondur ™ 582 (2.5 fn) 29.11% Trifunctionalcaprolactone polyol (CAPA 3031) (3.0 fn) 20.22% Water 0.67% **Niax ™L-1500 surfactant 0.04% *** KKAT ™ XK 614 catalyst 0.40% Dibutyl tindilaurate (T-12) 0.03% *Mondur ™ 582 (2.5 fn) - polymeric methylenediphenyl diisocyanate (p-MDI) with 2.5 functionality, available fromBayer Material Science. **Niax ™ L-1500 silicone-based surfactant,available from Momentive Specialty Chemicals, Inc. *** KKAT ™ XK 614zinc-based catalyst, available from King Industries.

Finally, the same ethylene acid copolymer ionomer composition used inExample A was molded over the intermediate ball to form a finished ballhaving a diameter of 1.680 inches. The properties of the golf balls madein Examples A and 1 above are set forth in Table II below.

TABLE II Properties of Finished Golf Balls Comparative- RubberComparative-Rubber Finished Ball Finished Ball Core and Foamed Core andSurlyn With Ionomer With Ionomer Rubber Core Intermediate LayerIntermediate Layer Outer Cover Outer Cover 1.530″ diameter 1.620″diameter 1.620″ diameter 1.680″ diameter 1.680″ diameter 35.83 gm. 40.71gm. 41.25 gm 45.73 gm 44.93 gm DCM - 77 DCM - 70 DCM - 88 DCM - 80 DCM -94 — 65 Shore C 94 Shore C 90 Shore C 94 Shore C surface hardnesssurface hardness hardness surface hardness CoR@125 ft./ CoR@125 ft./CoR@125 ft./ CoR@125 ft./ CoR@125 ft./ sec-0.793 sec-0.783 sec-0.812sec-0.798 sec-0.819

It is understood that the golf ball compositions, constructions, andproducts described and illustrated herein represent only someembodiments of the invention. It is appreciated by those skilled in theart that various changes and additions can be made to compositions,constructions, and products without departing from the spirit and scopeof this invention. It is intended that all such embodiments be coveredby the appended claims.

We claim:
 1. A multi-layered golf ball, comprising: i) an inner corecomprising a non-foamed thermoset or thermoplastic composition, theinner core having a specific gravity (SG_(inner)) and an outer surfacehardness (H_(inner core surface)) and a center hardness(H_(inner core center)), the H_(inner core surface) being the same orless than the H_(innercore center) to provide a zero or negativehardness gradient; ii) an intermediate layer comprising a foamedthermoset composition, the intermediate layer being disposed about thecore, the intermediate layer having a specific gravity (SG_(intermed.))and an outer surface hardness (H_(outer surface of intermed.)) and amidpoint hardness (H_(midpoint of intermed.)), theH_(outer surface of intermed.) being greater than theH_(midpoint of intermed.), to provide a positive hardness gradient;wherein the SG_(inner) is greater than the SG_(intermed.), theintermediate layer further having a specific gravity gradient, whereinthe intermediate layer has an outer surface specific gravity and amidpoint specific gravity, the outer surface specific gravity beinggreater than the midpoint specific gravity; and iii) a cover having atleast one layer disposed about the intermediate layer.
 2. The golf ballof claim 1, wherein the H_(inner core center) is in the range of about31 to about 95 Shore C and the H_(innercore surface) is in the range ofabout 30 to about 90 Shore C.
 3. The golf ball of claim 1, wherein the(H_(midpoint of intermed.)) is in the range of about 10 to about 55Shore C and the H_(outer surface of intermed.) is in the range of about11 to about 60 Shore C.
 4. The golf ball of claim 1, wherein the innercore comprises a thermoset rubber selected from the group consisting ofpolybutadiene, ethylene-propylene rubber, ethylene-propylene-dienerubber, polyisoprene, styrene-butadiene rubber, polyalkenamers, andbutyl rubber, and mixtures thereof.
 5. The golf ball of claim 1, whereinthe inner core comprises a thermoplastic polymer selected from the groupconsisting of partially-neutralized ionomers; highly-neutralizedionomers; polyesters; polyamides; polyamide-ethers, polyamide-esters;polyurethanes, polyureas; fluoropolymers; polystyrenes; polypropylenes;polyethylenes; polyvinyl chlorides; polyvinyl acetates; polycarbonates;polyvinyl alcohols; polyester-ethers; polyethers; polyimides,polyetherketones, polyamideimides; and mixtures thereof.